Fix typo [ci skip]

correct GlobalID mixin name in the guides

Update 2.7 & 2.8 of upgrading_ruby_on_rails.md [ci skip]

[ci skip] Fixes typos in section 2.7 "Rails Html Sanitizer", adds content to section 2.8 "Rails DOM Testing"

The email preview iframe height is fixed and does not scale to the browser size

On larger screens the email preview iframe is being limited to a height of 800 pixels, and the full available screen size is not being used.

document change_column and change_column_default for abstract_mysql_adapter [ci skip]

better example for tokenizer lambda [ci skip]

Splitting on whitespace makes more sense in the context of counting words in an
essay.

Added 'tzinfo-data' if we are using jruby

The MySQLAdapter type map used the lowest priority for enum types.
This was the result of a recent refactoring and lead to some broken lookups
for enums with values that match other types. Like `8bit`.

This patch restores the priority to what we had before the refactoring.

/cc @sgrif

This patch uniformizes warning messages. I used the most common style
already present in the code base:

* Capitalize the first word.

* End the message with a full stop.

* "Rails 5" instead of "Rails 5.0".

* Backticks for method names and inline code.

Also, converted a few long strings into the new heredoc convention.

let warn with heredocs

We were relying on hash inequality in tests

The query cache uses bind values as hash keys. The current
implementation relies on reference equality for hash equality. This is
brittle, and can easily break in the future.

We shouldn't rely on reference equality of these objects in tests

The current style for warning messages without newlines uses
concatenation of string literals with manual trailing spaces
where needed.

Heredocs have better readability, and with `squish` we can still
produce a single line.

This is a similar use case to the one that motivated defining
`strip_heredoc`, heredocs are super clean.

The value methods will default to an empty array for us automatically

The change to accessing keys directly was originally added to allow
`merge` to take a hash. The implementation of `HashMerger` no longer
requires us to be doing so. Accessing the values directly makes it
impossible to change internal storage details, even if shim methods are
added temporarily

Added ability to configure the queue_name_prefix delimiter to ActiveJob::QueueName.

In cases where this option is set to `true`, the option is redundant and can
be safely removed; otherwise, the corresponding `*_url` helper should be
used instead.

Fixes #17294.

See also #17363.

[Dan Olson, Godfrey Chan]

Fix doc markup for `NumberHelper`

The character "*" is unnecessary in option candidates.
This incorrect markup was injected in e8c9aeca .

Fix rbx generated Gemfile regex

Optimize TimeWithZoneTest#strftime

UrlGenerationError are not catched as 404 anymore

Allow Relation#rewhere to work with infinite range values

https://travis-ci.org/rails/rails/jobs/39190983#L460

 1) Failure:
 AppGeneratorTest#test_psych_gem
 [test/generators/app_generator_test.rb:495]:
 Expected /gem 'psych',\s+'~> 2.0', \s+platforms: :rbx/ to match <snip>
 http://git.io/uuLVag)\ngem 'psych', '~> 2.0', platforms: :rbx\n\n

Raises ArgumentError when try to define a scope without a callable