[Testing guide] Use "Fixtures API" instead of "fixture api".
[Testing guide] Using "Fixtures API" consistently

- In guides, "API" is used consistently instead of "api".
- Reason behind replacing "fixtures API" to "Fixtures API" is because
  here we are referring to the concept of "fixtures". In other places in
  the guide "fixture" OR "fixtures" is referred to the single or
  multiple instances of test data.
- This is also followup of https://github.com/rails/docrails/commit/aa9d1332b20305dd860b21a7ada06c5252bebad5#commitcomment-8497376.
Fix grammar on ActiveRecord::AttributeMethods doc.

[ci skip]
allow 'all' for :domain option in addition to :all
Don't remove mailer layouts files
Remove custom errors page section from the guides

This pattern is too problematic and introduces a lot of edge cases:

  * On 4.2, the issue https://github.com/rails/rails/issues/15124 is
    back again.
  * needs to define each action for each http status otherwise the
    router raises ActionController::RoutingError (No route matches).
  * If the router has `match "/*username",...` and some action is
    missing, Rails will pick up the "match" and try to do its job.
  * encourages people to copy & paste programming. Not DRY.

[ci skip]
Fix Sidekiq ActiveJob integration setup

* .connect on a Redis connection wasn't valid
* Reset logger after we're done testing for redis connection to avoid
  "closed stream" error when starting server for real from a fork
Hide potentially sensitive ActiveJob params from logs

* Show GlobalID instead of full object .inspect output
Merge branch 'master' of github.com:rails/rails
Only filter GIDable objects; remove cosmetic changes
Remove unused AV/test/fixtures/blog_public

The fixtures were added to support StaticTests in 401cd97 but
those tests were then removed in d5ad92ce.

If Travis CI is happy with this PR, then you can be sure that
those fixtures are not needed anymore.
Remove one AV fixture (duplicate of an AP fixture)

Both ActionPack and ActionView include `test/fixtures/functional_caching/fragment_cached_without_digest.html.erb`.

The [ActionPack file](https://github.com/rails/rails/blob/master/actionpack/test/fixtures/functional_caching/fragment_cached_without_digest.html.erb) is used by the tests.

The [ActionView file](https://github.com/rails/rails/blob/master/actionview/test/fixtures/functional_caching/fragment_cached_without_digest.html.erb) is not: it was introduced in eb23754e when some tests and
fixtures were moved from AP to AV, but no tests in AV uses the fixture.

Long story short: if Travis CI is happy with removing the fixture, you can
be sure that is not needed anymore!
Add `#verified` and `#valid_message?` to MessageVerifier

This commit adds a `#verified` method to
`ActiveSupport::MessageVerifier` which will return either `false` when
it encounters an error or the message. `#verify` continues to raise an
`InvalidSignature` exception on error.

This commit also adds a convenience boolean method on `MessageVerifier`
as a way to check if a message is valid without performing the
decoding.
Merge pull request #17872 from claudiob/remove-duplicate-functional-caching-fixture

Remove one AV fixture (duplicate of an AP fixture)
Merge pull request #17871 from claudiob/remove-unused-blog-public-fixtures

Remove unused AV/test/fixtures/blog_public
Remove unused AV/test/fixtures/happy_path

The `test/fixtures/happy_path/render_action/hello_world.erb` file was
introduced in 8ab37c7 for the `TestRenderAction` test.

That test was subsequently removed in 34f058e, so the fixture is not
used anymore.

If Travis CI is happy, then you can be sure the fixture can be removed.
Remove unused AV/test/fixtures/scope

The file `modgreet.erb` was added 8 years ago in 21187c0
and is not used anymore by any test.
Merge pull request #17877 from claudiob/remove-happy-path-fixture

Remove unused AV/test/fixtures/happy_path
Merge pull request #17878 from claudiob/remove-unused-modgreet-fixture

Remove unused AV/test/fixtures/scope
tests, move pg geometric tests out of `base_test`.