Fix third-party system libraries list in ActiveStorage::Preview [ci skip]

Add test case for `font_url`

Since test of `font_url` was not in Action View's test suite, so it added.

rails-ujs: Update README

Make various wording tweaks to cater to users who are viewing the README
on NPM. Notably, don't highlight Yarn specifically in the installation
instructions -- even though this is the preferred tool of choice
especially in the Ruby community, some people still use NPM (and,
really, ES2015+ syntax has nothing to do with NPM or Yarn).

Add link to Rack website [ci skip]

Resemble links to Bundler and Yarn,
based on feedback by @kamipo

[ci skip]

Remove unused `new_credentials_configuration`

`new_credentials_configuration` is no longer used since 081a6ac6f7fd929798481f9ee333fb92b441356c.

Fix broken link to recaptcha.net [ci skip]

The link to recaptcha.net returns a 404. As far as I can tell, the new
link ought to be to https://developers.google.com/recaptcha/ .

Currently `:api:` tag has leaked on the doc directly since RDoc doesn't
support `:api:` tag directive.

http://api.rubyonrails.org/v5.1/classes/AbstractController/Rendering.html

So `:api: private` doesn't work as expected. We are using `:nodoc:` for
the purpose.

Related #13989.

Remove unused methods from `RenderPartialWithRecordIdentificationController`

Follow up of #30728.

These methods no longer used since a3da293b.

Don't use Active Support where it is not needed.

Fix "warning: method redefined; discarding old test_scaffold_plural_names"

This code has been changed with https://github.com/rails/rails/pull/30735/files#diff-8e5f6b33c191ad6dec07f3288345a13fL47.

However, `active_support/time` is not load automatically, so if use
Action Pack alone, `days` method can not use and an error occurs.
In this case, I think that there is no problem by specifying a value
with Integer.

Since warning was issued due to duplication of test names, fix the test
name to a meaningful name.

This fixes following warnings:

```
railties/test/generators/named_base_test.rb:141: warning: method redefined; discarding old test_scaffold_plural_names
railties/test/generators/named_base_test.rb:62: warning: previous definition of test_scaffold_plural_names was here
```

https://travis-ci.org/rails/rails/jobs/281044755#L5582-L5586

Fix formatting in ActionDispatch::SSL middleware docs

Fix Typo in Testing Guide [ci skip]

Fixes for use_authenticated_cookie_encryption

See the changelog entry.

Remove `secrets.secret_token` from the bug report templates,
since we don't accept bug reports for Rails versions that
don't support a `secret_key_base`.

[ claudiob & Kasper Timm Hansen ]

Set version in activestorage/package.json in proper format.

Add assert_enqueued_email_with to ActionMailer::TestHelper

`5.2.0.alpha` => `5.2.0-alpha`

System versioning isn't compliant with npm.

Before: https://monosnap.com/file/J6xewF0tYpm6dC9nSTe82ddsHAOcM5.png

After: https://monosnap.com/file/0tCYicLXNqRHAEMDb81u0aLb3gH9Wf.png

[ci skip]

activerecord: Remove a redundant mutation tracker

Nested scaffold should be fine