Distinguish rake assets:clobber from rake assets:clean

[ci skip]

Replace `type_cast` case statement with delegation

Fix confusing exception in ActiveSupport delegation

Have Postgres OID types inherit from general types

Use general types for mysql fields

All subclasses of column were now delegating `type_cast` to their
injected type object. We can remove the overriding methods, and
generalize it on the `Column` class itself. This also enabled us to
remove several column classes completely, as they no longer had any
meaningful behavior of their own.

Delegate type_cast to injected type object in mysql

Using general types where possible. Several more can go away once
infinity gets figured out.

Delegate `#type_cast` to injected type objects on SQLite3

Fixed the inferred table name of a HABTM auxiliar

Fixes #14824.

Use generated binstubs in guides examples. [ci skip]

[ci skip]

While running Sqlite3 memory tests I encountered the following error:

```
Finished in 69.416366s, 58.0267 runs/s, 162.3681 assertions/s.

  1) Error:
ActiveRecord::Migration::ChangeSchemaTest#test_add_column_with_timestamp_type:
NoMethodError: undefined method `type' for nil:NilClass
    /Users/senny/Projects/rails/activerecord/test/cases/migration/change_schema_test.rb:244:in `test_add_column_with_timestamp_type'

4028 runs, 11271 assertions, 0 failures, 1 errors, 1 skips
```

This was because the table `testings` was used in multiple test-cases.
This resulted in a wrongly cached schema on `ActiveRecord::Base.schema_chae`.

/cc @zuhao

Closes #15122
Closes #15107

Un-define :to_json for Customer class after stubbing.

Deregister csv renderer after test to prevent leak.

This reverts commit 5c224de9.

Conflicts:
	actionpack/lib/action_dispatch/journey/visitors.rb

5c224de9 introduced a bug in the
formatter.  This commit includes a regression test.

Remove :timestamp column type

The `:timestamp` type for columns is unused. All database adapters treat
them as the same database type. All code in `ActiveRecord` which changes
its behavior based on the column's type acts the same in both cases.
However, when the type is passed to code that checks for the `:datetime`
type, but not `:timestamp` (such as XML serialization), the result is
unexpected behavior.

Existing schema definitions will continue to work, and the `timestamp`
type is transparently aliased to `datetime`.

Default config.assets.digests to true in development

Fix migrations that use enable_extension with table_name_prefix/suffix

Conflicts:
	activerecord/CHANGELOG.md
	activerecord/lib/active_record/migration.rb

Delegate `Column#type` to the injected type object

The decision to wrap type registrations in a proc was made for two
reasons.

1. Some cases need to make an additional decision based on the type
  (e.g. a `Decimal` with a 0 scale)
2. Aliased types are automatically updated if they type they point to is
  updated later. If a user or another adapter decides to change the
  object used for `decimal` columns, `numeric`, and `number` will
  automatically point to the new type, without having to track what
  types are aliased explicitly.

Everything else here should be pretty straightforward. PostgreSQL ranges
had to change slightly, since the `simplified_type` method is gone.

Return early on delete and destroy methods