Expose mono_class_is_open_constructed_type to Unity to allow us to check to see if the class is not yet fully instantiated prior to asttempting to call mono_object_new on it.

* Also cleaning up a minor leak of a MonoError in mono_unity_class_inflate_generic_class

There is a small race condition during the completion of a native thread join
call. During that period of time the tid is no longer included on the
internal list tracking joinable threads so a thread that will join on the
tid while another thread (like the finalizer thread) is waiting on native
join to complete for the same tid, will cause the managed Thread.Join call
to complete before the native join call has completed. This race could cause
issues on some OS:es that clear's up some thread resources, like abandoned
mutexes when the thread has exited. This race is hit by WaitAnyWithSecondMutexAbandoned
since the call to Thread.Join will return before the thread owning the mutex
has terminated meaning that it doesn't get ownership of the abandoned mutex
as assumed by the test.

Fix makes sure Thread.Join won't complete until native thread join is complete.
Increasing the join timeouts in the test also eliminates a timeout error making it
harder to hit the problematic code path, primarily during reproduction
in the debugger.

Fix also switch to coop mutex for joinable threads.

In managed, these functions are used as `static external IntPtr`. This means that previously on arm64 the top bits of the return value were garbage. A comparison with 64-bit -1 like in LinuxNetworkChange.EnsureSocket would never be true, which was causing us to hit other assertions in the runtime.
Co-authored-by: NAleksey Kliger <alklig@microsoft.com>

Allow `CreateDelegate` to have return type covariance with methods that
return `enum` or `int` types.

This is from the upstream change at https://github.com/mono/mono/commit/122494330d635205b0a8766deaeafd0d79bd3d60.

After adding the concept of a pending threads join list boehm was not removing the threads from that list on detach as sgen was in sgen_client_thread_detach_with_lock. This change brings boehm in line with sgen to remove threads from the pending join list on detach to avoid waiting the full 2 seconds on runtime shutdown. (case 1295072)

These changes are applied from upstream Mono at https://github.com/mono/mono/pull/7308/commits/e25f5c321573b677ab9edcb88833ef40d267026c.

They correct an exception that happens on Linux like this:

```
System.TypeInitializationException: The type initializer for 'System.Console' threw an exception. ---> System.TypeInitializationException: The type initializer for 'System.ConsoleDriver' threw an exception. ---> System.Exception: Magic number is wrong: 542
  at System.TermInfoReader.ReadHeader (System.Byte[] buffer, System.Int32& position) [0x0008d] in /Users/bokken/build/output/Unity-Technologies/mono/mcs/class/corlib/System/TermInfoReader.cs:134
  at System.TermInfoReader..ctor (System.String term, System.String filename) [0x0005f] in /Users/bokken/build/output/Unity-Technologies/mono/mcs/class/corlib/System/TermInfoReader.cs:97
  at System.TermInfoDriver..ctor (System.String term) [0x00055] in /Users/bokken/build/output/Unity-Technologies/mono/mcs/class/corlib/System/TermInfoDriver.cs:164
  at System.ConsoleDriver.CreateTermInfoDriver (System.String term) [0x00000] in /Users/bokken/build/output/Unity-Technologies/mono/mcs/class/corlib/System/ConsoleDriver.cs:73
  at System.ConsoleDriver..cctor () [0x0004d] in /Users/bokken/build/output/Unity-Technologies/mono/mcs/class/corlib/System/ConsoleDriver.cs:57
```

Pulling in change https://github.com/mono/mono/pull/12008/files which removes the registry as a dependecy for system.xml

Run codesign after otool

Ensure special static slots respect alignment (case 1266322)

Without proper alignment, this may lead to reference types
being stored at non-pointer aligned offsets. Among other
issues this may lead to the GC not scanning those pointers
properly.

Fix JIT on macOS Big Sur beta 6 when running on Apple silicon

Wait on runtime threads to park on joinable thread list during shutdown. (case 1275345)

Sign binaries after lipo-ing them since lipo drops signature added by the linker. Also, use JIT entitlement for signing executables.

Try to copy monodis into monodistribution/bin dir

Unity master fix case 1274470

Unity master fix case 1273662

Fixes https://github.com/mono/mono/issues/20367.

Some light massaging done by @UnityAlex to cherry pick

https://github.com/mono/mono/pull/5599 fixed a race condition during shutdown
when runtime threads have come parts of their way through detach, but still
depend on runtime resources, like GC memory. The fix added runtime threads
to the joinable thread list just before they vanished from mono_thread_manage
radar making sure shutdown waited upon the thread before cleaning up.

The above fix slightly changed the behavior of the finalizer thread since it
waits on joinable threads and will now potential block on threads still
executing code (that involves runtime resources). There’s was an assumption
around the threads on the joinable thread list that they should be very close
to complete when added, so join calls coming from the finalizer thread should
almost never block and if it does, the code that remains to execute should not
involve runtime operations risking deadlock situations. Adding the thread to
the list earlier than previously done expose the shutdown to some potential
theoretical problems.

To mitigate the risk and still solve the race condition this commit adds a
mechanism to keep track of active runtime threads until they park on joinable
thread list. The pending counter will be waited upon by the shutdown
thread, just before it does its regular wait on all joinable threads
(after finalizer thread has stopped) to make sure all runtime threads have
been added to the joinable thread list before waiting upon them. Threads are
added to the joinable thread as late as possible, exactly how it’s been done
in the past by sgen_client_thread_detach_with_lock. Shutdown thread will wait
on runtime threads to appear on the list for a short time and if timeout (pending
runtime thread count not reaching 0 before timeout), it will just print a warning
and continue shutdown.

Getting into a wait state during shutdown due to runtime threads not yet added to
joinable threads list should be very rare (hitting previous race condition that was rare),
triggering the timeout should be even more rare, and if that ever happens, we are exposed
to shutdown race condition as we have had in the past, but now we at least get a warning in
the log making it simpler to analyze further.

This commit also fixes a problem with the debugger thread hitting the same race condition as above.
The shutdown thread stopping the debugger thread didn't completely wait for it to stop using runtime
resources before continue shutdown sequence. This triggers the same race condition as when shutting
down regular runtime threads. This commit makes sure stop_debugger_thread waits on the debugger thread
handle to become signaled (happens at the very end of thread lifetime) before continuing the shutdown
logic.

Remove hack from mono_free_method. Bypassing cleanup here was causing corruption to persist in mscorlib's method hashtable when a rehash occurred.  Unity profiler may need changes to avoid possessing dangling pointers. Same with the mono profiler (as the comment indicates)

https://github.com/Unity-Technologies/mono/commit/7869333c52a2fc2d165effefdbbe97fdf9587b57
https://github.com/mono/mono/pull/9863
https://github.com/Unity-Technologies/mono/commit/f265d9a7838c97d33e8836dfc42d1f946de09041

Needed in order to fix corruption that was occuring to mscorlib's image table on domain reload due to dynamic methods from other images being stored in a hashtable that was not being cleaned up on domain reload.

The NetworkChange event is not supported on Windows (case 1278048)

Fix performance regression due to ldfld usage by Roslyn (case 1276888)

Provide a proper `PlatformNotSupported` exception for the
`NetworkChange` event on Windows, as it is not currently supported.

* Generalize commit 0c6932a9 to support LDARG{0|1|2|3}, LDLOC{0|1|2|3}, LDARGS, LDLOCS, LDARG and LDLOC instead of LDLOC and LDLOCS. Improves generated code similar to issue #60945

Grab part of fix from upstream change: https://github.com/mono/mono/p…

Branch for 2020.2 updates

Merge pull request #1335 from Unity-Technologies/unity-master-method-to-skip-assembly-version-validation

Add option to ignore versions when loading strong named assemblies