The fix for 1256569 broke a test. Reverting most of that change and breaking the CreateLocal -> WinRTFallback -> CreateLocal loop by calling GetLocalTimeZoneInfoWinRTFallback instead of accessing Local from within FindSystemTimeZoneByIdWinRTFallback fixes both issues.

Need to make sure we don't duplicate the timezone and create a new local when we already have one.

Fixing a hang that would occur when there is incorrectly set time zone data in the windows registry. (case 1256569)

TimeZoneNotFoundException. Added a catch to allow mono to try the WinRT
fallback which appears to work even when there is an invalid timezone
value in the registry.

The current class library code uses managed exceptions for flow control
for time zone handling. Specifically, it depends on exceptions to occur
if one of the files that _might_ have time zone information does not
exist.

On Android with IL2CPP we run into problems with C++ exceptions causing
hangs in some cases. Since IL2CPP implements managed exceptions using
C++ exceptions, this code can cause problems.

This change corrects Unity case 1100856.

Attempt to use Win32 APIs first to retreive current timezone. Registry value can be null/corrupt (case 1076679)

for some regions, specifically Asia/Singapore, the native icall returns incorrectly because the country's timezone changed. In this case in 1981 Asia/Singapore changed from +0730 to +08....Since the UTC offset changed, our logic thinks that daylight savings may have started, and the icall returns incorrect data, which causes the CreateLocalUnity function to throw.  Fixing the icall is important, but for the time being we'll wrap the CreateLocalUnity function with a try catch. then fix the native icall...

CreateLocal works by checking the platform. If it is windows, it uses the windows API or registry depending on api version, UWP, etc. otherwise it checks for the $TZ environment variable. If thats not found. it looks for /etc/localtime.....more obscure platforms like WebGL have no means of obtaining tzdata this way. This means that CreateLocal falls back to setting the TimeZoneInfo.Local time to UTC....this causes functions like DateTime.Now and DateTime.ToLocalTime to convert to UTC, instead of the user's local time.  By using Mono's old icall, we won't be able to convert between arbitrary timezones, but basic time conversion, such as UTC to Local will work.

This was hiding a bug reading registry info for some timezones.

This fixes creation of TimeZoneInfo for some time zones on Wine (such
as Israel Standard Time) and probably also Windows.

* Bug #56499: unreadable /etc/localtime should not cause an exception

* Fix build

This was breaking the hybrid AOT build.

* [corlib] Fixes static builds

* During the ambiguous hour .NET will return the DST version of the time whereas mono is returning the base time. Rather than use the transitions array we look up the Adjustment rules (which are created from the transition rules in the first place).

In addition, CurrentTimeToUtc() also has problems around the transition time.

Added test and fixed another.

Fixes #43805.

* Despite the tutorial on msdn about daylight saving time, .NET interprets the 'ambiguous' hour of DST as being DST rather than standard time which is what mono did.

Band aid fix until we can switch to CoreRT's implementation.

We decided it's a better name since we're using the profile to
test FullAOT scenarios on desktop (as opposed to the mobile profiles).

While doing the rename I saw that a lot of the #ifdefs were using
MOBILE_STATIC even though the code should actually be included/excluded
in all FullAOT scenarios, e.g. System.Reflection.Emit. I replaced those
cases with FULL_AOT_RUNTIME instead.

For cases where code is specific to this profile, I added a new
AOT_ONLY_DESKTOP define.

This only fixes the compilation of the assemblies and the tests. This doesn't fix the failing tests or the crashes.

TimeZoneInfo.GetDaylightChanges() didn't work as expected when run against the
time zone data available in Windows.

This patch also enables most of the time zone related tests that were
previously ignored when not run on Unix platforms. Time zone ids will now be
mapped from tz db time zone names to Windows time zone names when needed so
that most of the tests can be run on Mono on Windows as well.

behaviour when passed times within the lost period at DST start

When passed a time within this period .NET's IsDaylightSavingTime() returns
true while GetUtcOffset() returns the BaseUtcOffset without the DST delta
added. This patch changes the behaviour in Mono to do what .NET does.

NET_2_1 is also defined whenever we define MOBILE, so they have the same effect. Silverlight was 2.1 but it's been dead for a while now, and we do not even support it.

Fixes #41349

[mscorlib] Better handling of unix timezones which have offset not specified in whole minutes. Fixes #41492

Such as "Central Standard Time (Mexico)"

Previously this caught only cases where libc was absent, now it catches cases where libc is present but does not contain readlink

Context: https://bugzilla.xamarin.com/show_bug.cgi?id=31432

In a few android devices TimeZoneInfo.ParseTZBuffer was failing ito
parse Europe/Moscow with:
at System.ThrowHelper.ThrowKeyNotFoundException ()
at System.Collections.Generic.Dictionary`2[System.Int32,System.String].get_Item (Int32 key)mscorlib/system/collections/generic/dictionary.cs:176
at System.TimeZoneInfo.ParseTimesTypes (System.Byte[] buffer, Int32 index, Int32 count, System.Collections.Generic.Dictionary`2 abbreviations) [0x0002f] in mcs/class/corlib/System/TimeZoneInfo.cs:1293
at System.TimeZoneInfo.ParseTZBuffer (System.String id, System.Byte[] buffer, Int32 length)

It was failing while getting the third index [3] from] from abbrevs.

abbrevs added values were the following:
[0, MMT]
[1, MT]
[2, T]
[4, MST]
[5, ST]
[6, T]
[8, MDST]
[9, DST]
[10, ST]
[11, T]
[13, S]
[15, M]
[17, MSK]
[18, SK]
[19, K]
[21, EET]
[22, ET]
[23, T]
[25, MSD]
[26, SD]
[27, D]
[29, EEST]
[30, EST]
[31, ST]
[32, T]

Index 3 was not added because its values is an empty string, as indexes
with empty values are used in this case we are now adding them to the
abbrevs dictionary.

Fixes #31432

Fixes TimeZoneInfo.ConvertTimeFromUtc and related tests when
TimeZoneInfo.Local is equal to TimeZoneInfo.Utc.

In .NET if we set TimeZoneInfo.Local to TimeZoneInfo.Utc by using
reflection.

```
var cachedDataField = typeof (TimeZoneInfo).GetField ("s_cachedData",
BindingFlags.Static | BindingFlags.GetField | BindingFlags.NonPublic);

var localField = cachedDataField.FieldType.GetField ("m_localTimeZone",
BindingFlags.Instance | BindingFlags.GetField | BindingFlags.NonPublic);

var localFieldObj = cachedDataField.GetValue (null);

localField.SetValue (localFieldObj, DateTimeKind.Utc);
```

We can observe that `TimeZoneInfo.ConvertTimeFromUtc (DateTime.UtcNow,
TimeZoneInfo.Local).Kind` is DateTimeKind.Utc.

By looking at reference source [code](http://referencesource.microsoft.com/#mscorlib/system/timezoneinfo.cs,211)
we can also confirm that while getting a time zone corresponding kind,
Utc is prioritized over Local.

This commit reverts changes introduced by
60d5b39e that were prioritizing Local
over Utc and changes tests to expect Utc kinds instead of Local when
TimeZoneInfo.Local is equal to TimeZoneInfo.Utc.

TimeZoneInfo.ConvertTimeFromUtc(utcDate, TimeZoneInfo.Local) now returns a date of kind
DateTimeKind.Local when TimeZoneInfo.Local is equal to TimeZoneInfo.Utc.

Fixes #33471.

See https://bugzilla.xamarin.com/show_bug.cgi?id=30360

Fixes #32722.

A private overload of the public GetSystemTimeZones() method was added in 4dc9a90d.
This broke code that tried to access that method via reflection and expected that there be only one.

Fixing this by renaming the private method to GetSystemTimeZonesCore (which is also more aligned with FindSystemTimeZoneByIdCore).

TimeZoneInfo.Local.Id now returns a Olson id when "/etc/localtime" is a
symbolicate link instead of "Local".

Fixes #24958.