Refactor AR's validations_test.rb

The `:context` switch feature is implemented in
ActiveRecord::Validations#valid? method, so we should rename the test
names, and execute `valid?` in the test.

Change test name in AR's validations_test.rb

This test is testing save method's code
Allow custom asset host to be passed in asset_url
Improve documentation for asset_url

Updated CHANGELOG.md with entry about :host in asset_url
Fixed duplicate subscribers in ActiveSupport::Subscriber

ActiveSupport::Subscriber no longer creates multiple subscribers when
you redefine a method.
Add controller and action name to the instrumentation payload
minor change in AR readme [ci skip]
feature detect for FNM_EXTGLOB for older Ruby. Fixes #15053
Keep method's description/documentation consistent [ci skip]
Merge pull request #15054 from mechanicles/documentation-consistency

Keep method's description/documentation consistent [ci skip]
Change Gemfile’s double quotes in plugin generator

Since the generated application’s Gemfile is using single quotation marks, it
seems fair to use it on plugin’s Gemfile as well.
Merge pull request #15056 from josemarluedke/single-quotes-on-plugin-gemfile

Change Gemfile’s double quotation marks in plugin generator
docs, fix typo in docs added by ed56e596a04673. [ci skip]
pg guide, PostgreSQL legacy table view example. [ci skip]
ActionDispatch::Http::URL.normalize_port should not strip port for protocol relative URL.
Always use the provided port for protocol relative urls

There may be situations where you need to tunnel SSL connections over
port 80 so we shouldn't remove it if it has been explicitly provided.
Merge branch 'master' of github.com:rails/rails
adding complete message in documentation [ci skip]
Merge pull request #15058 from Gaurav2728/gaurav-doc_message

adding complete message in documentation [ci skip]
docs, make `ActionNotFound` public API. [ci skip]

This is a follow up to #15058.

This exception is regularly raised during development. This means it will enter
the user realm. We should provide an API page to show that this exception is public API.

/cc @schneems
Make TimeZone#parse behave more like Time#parse.

Namely, if the mday is omitted but any other upper components are, then instead
of supplying the mday from the current time, it defaults to 1.