[ActionCable] test perform action with default action

This test needs to have a require for the Listen gem or else it returns
an error when run by itself or with a certain order in the Active
Support tests. We use `silence_warnings` because Listen has some
warnings about private methods. It's already silenced when it's required
in Active Support EventedFileUpdateChecker.

```
1) Error:
EventedFileUpdateCheckerTest#test_should_not_execute_the_block_if_no_paths_are_given:
NameError: uninitialized constant EventedFileUpdateCheckerTest::Listen
    test/evented_file_update_checker_test.rb:21:in `teardown'
```

The test was was in here twice so we were seeing this error:

```
activesupport/test/caching_test.rb:658:
warning: method redefined; discarding old test_local_cache_of_read_nil
activesupport/test/caching_test.rb:634:
warning: previous definition of test_local_cache_of_read_nil was here
```

Fix "instance variable not initialized" in tests

Prevent ActionController::Parameters in url_for

add line break between method of generated channel js

[ActionCable] Test available actions on Channel

Our logic is complex now and we don't need to check the version to asset
the behavior so I'm removing the checking here.

Allow normal version updates within a release series

Still more to do. Please assist!

We went back to `Thread.current[]` in 33e11e59.

[ci skip] Fix grammar

```
# before
App.appearance = App.cable.subscriptions.create "AppearanceChannel",
  connected: ->
    # Called when the subscription is ready for use on the server

  disconnected: ->
    # Called when the subscription has been terminated by the server

  received: (data) ->
    # Called when there's incoming data on the websocket for this channel

  appear: ->
    @perform 'appear'
  away: ->
    @perform 'away'
```

```
# after
App.appearance = App.cable.subscriptions.create "AppearanceChannel",
  connected: ->
    # Called when the subscription is ready for use on the server

  disconnected: ->
    # Called when the subscription has been terminated by the server

  received: (data) ->
    # Called when there's incoming data on the websocket for this channel

  appear: ->
    @perform 'appear'

  away: ->
    @perform 'away'
```

This reverts commit 301f4382 per @matthewd on https://github.com/rails/rails/pull/22630/files#r47997074

fix indentation of generated controller test

```
# before
module Bukkits
  class UsersControllerTest < ActionDispatch::IntegrationTest
    include Engine.routes.url_helpers

      setup do
      @user = bukkits_users(:one)
    end
```

```
# after
module Bukkits
  class UsersControllerTest < ActionDispatch::IntegrationTest
    include Engine.routes.url_helpers

    setup do
      @user = bukkits_users(:one)
    end
```

We originally chose to apply very strict versioning on the `rails` entry
in the Gemfile, because our future versioning policy was not strongly
defined.

Now it is, and our policy is very much designed on the expectation that
people will regularly update to the latest patch level in their release
series... so we should encourage that.

Of course, Gemfile.lock will do its job and prevent unplanned updates,
just as it does for every other gem in the bundle... but if you run
`bundle update`, we want to get you the latest bug/security fixes
without requiring a manual edit of the Gemfile entry.

Our current version could be a few different shapes, so it takes a bit
of work to find the right specifier, but in principle, we match anything
of the form x.y.*, where x.y matches our current release series.

This file is generated by a gem that is bundled by default in the generated Rails app, just like .sqlite3 files.
Hence it might be natural to be ignored here rather than in each developer's .gitignore_global.

Document when fallback_location is used [ci-skip]