A querystring value should be allowed to include an equal sign `=`.

This is necessary to support passing `options` for a PostgresSQL connection.

```

development:
  url: postgresql://localhost/railsdevapp_development?options=-cmysetting.debug=on
```

Before this PR, attempting to start the rails process with that configuration would result in an error:

```
> bundle exec rails console
Traceback (most recent call last):
	49: from bin/rails:4:in `<main>'
	48: from bin/rails:4:in `require'
...
	 1: from /rails/activerecord/lib/active_record/database_configurations/connection_url_resolver.rb:58:in `query_hash'
/rails/activerecord/lib/active_record/database_configurations/connection_url_resolver.rb:58:in `[]': invalid number of elements (3 for 1..2) (ArgumentError)
```

After this PR, rails can properly parse the configuration:

```
> bundle exec rails console
Loading development environment (Rails 6.1.0.alpha)
2.6.5 :001 > ActiveRecord::Base.connection.select_all("show mysetting.debug").to_a
   (0.4ms)  show mysetting.debug
 => [{"mysetting.debug"=>"on"}]
```

Added posibility to open a `read_uncommitted` transaction on SQLite:

Don't run AJ after_enqueue / after_perform when chain is halted:

- ### Problem

  ```ruby
    MyJob < ApplicationJob
      before_enqueue { throw(:abort) }
      after_enqueue { # enters here }
    end
  ```
  I find AJ behaviour on after_enqueue and after_perform callbacks
  weird as they get run even when the callback chain is halted.
  It's counter intuitive to run the after_enqueue callbacks even
  though the job wasn't event enqueued.

  ### Solution

  In Rails 6.2, I propose to make the new behaviour the default
  and stop running after callbacks when the chain is halted.
  For application that wants this behaviour now or in 6.1
  they can do so by adding the `config.active_job.skip_after_callbacks_if_terminated = true`
  in their configuration file.

Fix ActiveJob logging when callback chain is halted:

- ### Problem

  ActiveJob will always log "Enqueued MyJob (Job ID) ..." even
  if the job doesn't get enqueued through the adapter.
  Same problem happens when performing a Job, "Performed MyJob (Job ID) ..." will be logged even when job wasn't performed at all.
  This situation can happen either if the callback chain is terminated
  (before_enqueue throwing an `abort`) or if an exception is raised.

  ### Solution

  Check if the callback chain is aborted/exception is raised, and  log accordingly.

- SQlite allow database to be specified as URL (given that URI filename
  interpretation was turned on on the connection.)

  This commit is necessary for the read_uncommitted transaction
  feature because SQLite doesn't allow to enable the shared-cache mode
  if the database name is `:memory:`. It has to be a URI (`file::memory`)

  Ref https://www.sqlite.org/sharedcache.html#shared_cache_and_in_memory_databases

- ### Use case

  I'd like to be able to see changes made by a connection writer
  within a connection reader before the writer transaction commits
  (aka `read_uncommitted` transaction isolation level).

  ```ruby
  conn1.transaction do
    Dog.create(name: 'Fido')
    conn2.transaction do
      Dog.find(name: 'Fido') # -> Can't see the dog untill conn1 commits the transaction
    end
  end
  ```

  Other adapters in Rails (mysql, postgres) already supports multiple
  types of isolated db transaction.
  SQLite doesn't support the 4 main ones but it supports
  `read_uncommitted` and `serializable` (the default one when opening
  a transaction)

  ### Solution

  This PR allow developers to open a `read_uncommitted` transaction by
  setting the PRAGMA `read_uncommitted` to true for the duration
  of the transaction. That PRAGMA can only be enabled if the SQLite
  connection was established with the [shared-cache mode](https://www.sqlite.org/sharedcache.html)

  This feature can also benefit the framework and we could potentially
  get rid of the `setup_shared_connection_pool` inside tests which
  was a solution in the context of a multi-db app so that the reader
  can see stuff from the open transaction writer but has some [caveats](https://github.com/rails/rails/issues/37765#event-2828609021).

  ### Edge case

  Shared-cache mode can be enabled for in memory database as well,
  however for backward compatibility reasons, SQLite only allows
  to set the shared-cache mode if the database name is a URI.
  It won't allow it if the database name is `:memory`; it has to be
  changed to `file::memory` instead.

This reverts commit 4e105385, reversing
changes made to 62b43839.

The change in Ruby that made those changes required was reverted in
https://bugs.ruby-lang.org/projects/ruby-trunk/repository/git/revisions/8852fa876039ed177fd5e867f36177d8a9ff411c

Rails::Application#config_for merges shared configuration deeply

[ci skip]

Add a yellow "NOTE" block to see if the guide looks better.

Remove unused query params in DiskService

Use DiskController for both public and private files

Bring back feature that allows loading external route files:

= This feature existed back in 2012 https://github.com/rails/rails/commit/5e7d6bba79393de0279917f93b82f3b7b176f4b5
  but got reverted with the incentive that there was a better approach.
  After discussions, we agreed that it's a useful feature for apps
  that have a really large set of routes.
Co-authored-by: NYehuda Katz <wycats@gmail.com>

I added myself links to the Ruby on Rails Tutorial years ago, after
meeting Michael in a RailsConf.

By then, the book was a commercial product, but had a free online
version and I thought it could be a good resource complementing the
official documentation.

Nowadays, only a few sample chapters are available for free, and I
don't consider these links to be fair with the rest of commercial
books about Rails anymore.

Revert "Use `app.config.file_watcher` for watcher in `RoutesReloader`"

This reverts commit 28e44f47.

A limitation of Listen is that it currently only supports watching directories.
Therefore, watching `config/routes.rb` will end up watching the entire `config` directory
if we use the evented file watcher. This causes problems especially if symlinks are present
in the `config` directory.

system tests: properly set driver options for non-headless drivers

Use `app.config.file_watcher` for watcher in `RoutesReloader`

Upgrade listen to 3.2.1 for darwin fixes

Pulls in a fix where the darwin adapter no longers create a `fsevent_watch` process
for each directory that Listen has been asked to watch.

Closes #37666