Make get_value public again

Adds test case for failing issue

Moves set_value back to protected

Fix title for example of removing data from `session` [ci skip]

Fix segmentation fault in EventedFileUpdateChecker

Break up Journey's scanner test

Address `NameError: uninitialized constant Arel::Collectors::Bind`

when tested with Ruby 2.5 or higher

```ruby
$ ruby -v
ruby 2.5.1p57 (2018-03-29 revision 63029) [x86_64-linux]
$ bundle exec ruby -w -Itest test/cases/arel/collectors/bind_test.rb -n test_compile_gathers_all_bind_params
Run options: -n test_compile_gathers_all_bind_params --seed 24420

E

Error:
Arel::Collectors::TestBind#test_compile_gathers_all_bind_params:
NameError: uninitialized constant Arel::Collectors::Bind
Did you mean?  Binding
    test/cases/arel/collectors/bind_test.rb:15:in `collect'
    test/cases/arel/collectors/bind_test.rb:19:in `compile'
    test/cases/arel/collectors/bind_test.rb:31:in `test_compile_gathers_all_bind_params'

bin/rails test test/cases/arel/collectors/bind_test.rb:30

Finished in 0.002343s, 426.8559 runs/s, 0.0000 assertions/s.
1 runs, 0 assertions, 0 failures, 1 errors, 0 skips
$
```

It is likely due to Ruby 2.5 does not look up top level constant.
https://www.ruby-lang.org/en/news/2017/12/25/ruby-2-5-0-released/
"Top-level constant look-up is no longer available."

Merge Arel

This breaks up the one megatest for Journey's scanner into multiple test
cases, which also provides better output when there is a failure in the
scanner.

Before:

```
./bin/test test/journey/route/definition/scanner_test.rb
Run options: --seed 778

F

Failure:
ActionDispatch::Journey::Definition::TestScanner#test_tokens [/Users/vaidehijoshi/Code/tilde/rails/actionpack/test/journey/route/definition/scanner_test.rb:57]:
--- expected
+++ actual
@@ -1 +1 @@
-[[:SLASH, "/"], [:LITERAL, "page!!"]]
+[[:SLASH, "/"], [:LITERAL, "page!"]]

bin/test Users/vaidehijoshi/Code/tilde/rails/actionpack/test/journey/route/definition/scanner_test.rb:14

Finished in 0.090899s, 11.0012 runs/s, 44.0049 assertions/s.
1 runs, 4 assertions, 1 failures, 0 errors, 0 skips
```

After:

```
./bin/test test/journey/route/definition/scanner_test.rb
Run options: --seed 2230

....................F

Failure:
ActionDispatch::Journey::Definition::TestScanner#test_scanning_/page$ [/Users/vaidehijoshi/Code/tilde/rails/actionpack/test/journey/route/definition/scanner_test.rb:58]:
Wrong tokens for `/page$`.
--- expected
+++ actual
@@ -1 +1 @@
-[[:SLASH, "/"], [:LITERAL, "page$$"]]
+[[:SLASH, "/"], [:LITERAL, "page$"]]

bin/test Users/vaidehijoshi/Code/tilde/rails/actionpack/test/journey/route/definition/scanner_test.rb:56

F

Failure:
ActionDispatch::Journey::Definition::TestScanner#test_scanning_/page! [/Users/vaidehijoshi/Code/tilde/rails/actionpack/test/journey/route/definition/scanner_test.rb:58]:
Wrong tokens for `/page!`.
--- expected
+++ actual
@@ -1 +1 @@
-[[:SLASH, "/"], [:LITERAL, "page!!"]]
+[[:SLASH, "/"], [:LITERAL, "page!"]]

bin/test Users/vaidehijoshi/Code/tilde/rails/actionpack/test/journey/route/definition/scanner_test.rb:56

F

Failure:
ActionDispatch::Journey::Definition::TestScanner#test_scanning_/page& [/Users/vaidehijoshi/Code/tilde/rails/actionpack/test/journey/route/definition/scanner_test.rb:58]:
Wrong tokens for `/page&`.
--- expected
+++ actual
@@ -1 +1 @@
-[[:SLASH, "/"], [:LITERAL, "page&&"]]
+[[:SLASH, "/"], [:LITERAL, "page&"]]

bin/test Users/vaidehijoshi/Code/tilde/rails/actionpack/test/journey/route/definition/scanner_test.rb:56

Finished in 0.126447s, 181.8944 runs/s, 181.8944 assertions/s.
23 runs, 23 assertions, 3 failures, 0 errors, 0 skips
```

We don't use `mini_magick` directly since #32471.

resolves #32705

Fix typo in migrations guide [ci skip]

Introduced in #32646

Update schema.rb documentation [CI SKIP]

The documentation previously claimed that `db/schema.rb` was "the
authoritative source for your database schema" while simultaneously
also acknowledging that the file is generated. These two statements are
incongruous and the guides accurately call out that many database
constructs are unsupported by `schema.rb`. This change updates the
comment at the top of `schema.rb` to remove the assertion that the file
is authoritative.

The documentation also previously referred vaguely to "issues" when
re-running old migrations. This has been updated slightly to hint at the
types of problems that one can encounter with old migrations.

In sum, this change attempts to more accurately capture the pros, cons,
and shortcomings of the two schema formats in the guides and in the
comment at the top of `schema.rb`.

[Derek Prior & Sean Griffin]
Co-authored-by: NSean Griffin <sean@seantheprogrammer.com>

https://github.com/sparklemotion/sqlite3-ruby/blob/v1.3.13/lib/sqlite3/statement.rb#L101-L104

Use strict_encode64 instead of gsub newline for ScreenshotHelper

Save a hash allocation in MySQL statement pool

Ensure that other processes like ImageMagick and FFmpeg see the complete contents of the file.

Use ImageProcessing gem for ActiveStorage variants

There's no need to wrap the statement in a hash with a single key.

Halve memory allocation in S3Service#download

Aws::S3::Object#get returns a response with object content wrapped in an
in-memory StringIO object. StringIO#read will return a copy of the
content, which is not necessary because we can return the content
directly using StringIO#string. This halves memory allocation of
S3Service#download, because we remove unnecessary content duplication.

After #31685 the description says different what
we expect to see in the example. Change `assign that key to be nil` to
`or delete the key/value pair` in order to highlight what is shown in the example.

Fix one more example of removing data from the session in favour of using
`delete` since assigning to `nil` doesn't delete key from it.

* Remove key from session by using session.delete

You are not deleting a key from session when you assign nil to that key.

* Update guides on how to destroy a user session

In this commit, the user id is removed from session and controller's variables related to the user are nullified.

[Rafael Mendonça França + Rafael Barbolo]

Update rails-ujs readme

This is not true anymore, the image will be downloaded into a temporary
file in a streaming fashion.

Since other views use the `h2` tag, should also use `h2` on
`missing_exact_template.html.erb`.

https://github.com/rails/rails/blob/76acaf6eb9ef3635e4c6f2ca9dba34edb50f541d/actionpack/lib/action_dispatch/middleware/templates/rescues/routing_error.html.erb#L5
https://github.com/rails/rails/blob/76acaf6eb9ef3635e4c6f2ca9dba34edb50f541d/actionpack/lib/action_dispatch/middleware/templates/rescues/diagnostics.html.erb#L11
https://github.com/rails/rails/blob/76acaf6eb9ef3635e4c6f2ca9dba34edb50f541d/actionpack/lib/action_dispatch/middleware/templates/rescues/unknown_action.html.erb#L5

Update results of command in Testing guides [ci skip]

Refactor guides javascripts