Update Action Cable Overview Guide [ci skip]

Fix CustomUrls#direct doc formatting

Particularly, the bulleted list was getting formatted as a code block because of the extra level of indentation.  Pulling it back to the left makes it render properly as a list instead.

[ci skip]

Update incorrect backtick usage in RDoc to teletype

[ci skip]

Fix generator suggestion raise error when I18n.available_locales don’t include :en

FIX: `rack-test` 0.7.1 probably got yanked.

`em-hiredis` is unused since 48766e32

Permit creating a record and attaching files in a single step.

    # Before:
    User.create!(user_params.except(:avatar)).tap do |user|
      user.avatar.attach(user_params[:avatar])
    end

    # After:
    User.create!(user_params)

[Yoshiyuki Hirano & George Claghorn]

Support `expires_in` in `ActiveSupport::Cache::MemCacheStore#increment`
and `#decrement`.

Closes #30716.

Disable CSRF protection for ActiveStorage::DiskController#update. The local disk service is intended to imitate a third-party service like S3 or GCS, so we don't care where direct uploads originate: they’re authorized by signed tokens.

Closes #30290.

[Shinichi Maeshima & George Claghorn]

Pass over Execution guide[ci skip]

[ci skip] Added example for using headless_chrome with SystemTest

Closes #31164.

These extra `spawn` are called via `klass.all` and `klass.all` is called
everywhere in the internal. Avoiding the extra `spawn` makes` klass.all`
30% faster for STI classes.

https://gist.github.com/kamipo/684d03817a8115848cec8e8b079560b7

```
Warming up --------------------------------------
       fast relation     4.410k i/100ms
       slow relation     3.334k i/100ms
Calculating -------------------------------------
       fast relation     47.373k (± 5.2%) i/s -    238.140k in   5.041836s
       slow relation     35.757k (±15.9%) i/s -    176.702k in   5.104625s

Comparison:
       fast relation:    47373.2 i/s
       slow relation:    35756.7 i/s - 1.32x  slower
```

https://travis-ci.org/rails/rails/jobs/304428814#L1977

Due to https://github.com/rack-test/rack-test/commit/5fd3631078e7c73aaed7d4371f70fb2a79384be9.

`keys_to_names` is used only for `keys_to_names.keys`.

Ref: https://travis-ci.org/rails/rails/jobs/303840778#L1974

Since fbd1e98c, Rails plugin does not
run `bundle install` when generating.
Therefore, `after_bundle` callback is not actually executed after `bundle`.

Since there is a difference between the name and the actual behavior,
I think that should be remove.

Prevent deadlocks with load interlock and DB lock.

Switch to LIFO for the connection pool

Enable query cache on all connection pools

Document public hooks in AS::Reloader

Move back to resque-scheduler mainline now that https://github.com/resque/resque-scheduler/pull/620 is merged

Fix links [ci skip]

Currently `_create_record` and `_update_record` in `Persistence` are
creating extra `unscoped` and calling `build_arel` in the relation. But
`compile_insert` and `compile_update` can be done without those
expensive operation for `SelectManager` creation. So I moved the
implementation to `Persistence` to avoid creating extra relation and
refactored to avoid calling `build_arel`.

https://gist.github.com/kamipo/8ed73d760112cfa5f6263c9413633419

Before:

```
Warming up --------------------------------------
      _update_record   150.000  i/100ms
Calculating -------------------------------------
      _update_record      1.548k (±12.3%) i/s -      7.650k in   5.042603s
```

After:

```
Warming up --------------------------------------
      _update_record   201.000  i/100ms
Calculating -------------------------------------
      _update_record      2.002k (±12.8%) i/s -      9.849k in   5.027681s
```

30% faster for STI classes.

Start on a guide for the Executor & Load Interlock