[ci skip] Fix rails/command.rb document

Latest `webdrivers` is necessary to run ujs test.

`split(/\s*,\s*/)` to order args and then `permit.match?` one by one is
much slower than `permit.match?` once.

Fix installation on guides/source/action_text_overview.md

gem 'image_proccessing' is required.

Add forgotten nodoc to dump_schema method.

Method added in https://github.com/rails/rails/pull/36416

There is no need to be wrapped by `Arel.sql()`.

Fix preloading on AR::Relation where records are duplicated by a join

Run actionview tests in parallel

Include warning in docs about polymorphism in underlying tables

We had a bug whereby we changed the namespace on a model using ActiveStorage, which resulted in broken download links. The reason this happened is because the `active_storage_attachments` table is a polymorphic join table that records the model's class name at the time of record creation, and uses this `record_type` in queries. Since the model namespace changed, the queries did not return the blob as expected. Discussed with @rafaelfranca, who suggested adding a warning about this in the docs.

Allow `on_rotation` in MessageEncryptor to be passed in constructor:

- Use case:

  I'm writing a wrapper around MessageEncryptor to make things easier
  to rotate a secret in our app.

  It works something like
  ```ruby
  crypt = RotatableSecret.new(['old_secret', 'new_secret'])
  crypt.decrypt_and_verify(message)
  ```

  I'd like the caller to not have to care about passing the
  `on_rotation` option and have the wrapper deal with it when
  instantiating the MessageEncryptor object.

  Also, almost all of the time the on_rotation should be the same when
  rotating a secret (logging something or StatsD event) so I think
  it's not worth having to repeat ourselves each time we decrypt a message.

Fixed a couple of typos, word 'deliberately' and database_resolver_context class name. [ci skip]

Bump rubocop to 0.71

Allow quoted identifier string as safe SQL string

Unlock `selenium-webdriver` gem version

Since `selenium-webdrive` v3.1.30, use `goog:chromeOptions'` key for
sending chrome options.
Ref: https://github.com/SeleniumHQ/selenium/commit/0ba8188b1a26ff3587f08afa6b6182c32479e980

`selenium-webdriver` is deprecateing various features for improvement in 4.0.
I want to test with the latest version to check if Rails uses deprecated
features or not.

We shouldn't modify fixtures (or any files which are checked-in). It
prevents us from parallelizing, and probably has other issues.

We could fix these tests by copying the file to a tmpdir and modifying
it there, but I don't think they are testing anything useful anymore.
Re-initializing a resolver isn't representative of "uncached" rendering
(either in dev-mode or using lookup_context.disable_cache).

Move schema cache to pool

This PR proposes moving the schema cache from the connection to the pool
so the connection can ask the pool for the cache. In a future PR our
goal is to be able to read the yaml file from the pool so we can get
rid of the `active_record.check_schema_cache_dump` initializer. This
will fix the issues surrounding dumping the schema cache and mulitple
databases.

Why do we want to get rid of the initializer you ask?

Well I was looking at #34449 and trying to make it work for our usecase
and it revealed A LOT of problems. There are a few issues that I will
fix in remaining PRs with SchemaMigration, but there's a big glaring
issue with this initializer.

When you have an application with multiple databases we'll need to loop
through all the configurations and set the schema cache on those
connections. The problem is on initialization we only have one
connection - the one for Ar::Base. This is fine in a single db
application but not fine in multi-db. If we follow the pattern in #34449
and establish a connection to those other dbs we will end up setting the
cache on the _connection object_ rather than on all connections that
connect for that config.

So even though we looped through the configs and assigned the cache the
cache will not be set (or will be set wrong) once the app is booted
because the connection objects after boot are _different_ than the
connection objects we assigned the cache to.

After trying many different ways to set the schema cache `@tenderlove`
and I came to the conclusion that the initializer is problematic, as is
setting the schema cache twice.

This is part 1 to move the cache to the pool so the cache can read from
the schema cache yaml file instead of setting it when initializing the
app.

To do this we have created a `NullPool` that initializes an empty cache. I
put the `get_schema_cache` and `set_schema_cache` in an `AbstractPool`
so we can share code between `ConnectionPool` and `NullPool` instead of
duplicating code.

Now we only need to set the schema_cache on the pool rather than the
connection. In `discard!` we need to unset the connection from the
schema_cache - we still want the cache just not the connection.

Currently `posts.title` is regarded as a safe SQL string, but
`"posts"."title"` (it is a result of `quote_table_name("posts.title")`)
is regarded as an unsafe SQL string even though a result of
`quote_table_name` should obviously be regarded as a safe SQL string,
since the column name matcher doesn't respect quotation, it is a little
annoying.

This changes the column name matcher to allow quoted identifiers as safe
SQL string, now all results of the `quote_table_name` are regarded as
safe SQL string.

Name helper_method module and improve source location

Fixed db:prepare task for multiple databases.

Treat ActiveRecord::Base and ApplicationRecord as "primary"

When someone has a multi-db application their `ApplicationRecord` will
look like:

```ruby
class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true

  connects_to database: { writing: :primary, reading: :replica }
end
```

This will cause us to open 2 connections to ActiveRecord::Base's
database when we actually only want 1. This is because Rails sees
`ApplicationRecord` and thinks it's a new connection, not the existing
`ActiveRecord::Base` connection because the
`connection_specification_name` is different.

This PR changes `ApplicationRecord` classes to consider themselves the
same as the "primary" connection.

Fixes #36382

When one database existed already, but not the other,
during setup of missing one, existing database was wiped out.

Guides 6.0 release notes: fix typo

An unfinished parenthetical.