Columns and injected types no longer have any conditionals based on the
format of SQL type strings! Hooray!

Ideally types will be usable without having to specify a sql type
string, so we should keep the information related to parsing them on the
adapter or another object.

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`.

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.

Part of #15134. In order to perform typecasting polymorphically, we need
to add another argument to the constructor. The order was chosen to
match the `oid_type` on `PostgreSQLColumn`.

this lets arel know how to correctly quote the value

This method is not being called anywhere in our code and a GitHub search
show it is not being used in any project.

These comments will likely be outdated with time and doesn't include
any information that can't be found in the adapters

This is important, because adding an index on a temporary table after
it has been created would commit the transaction

Conflicts:
	activerecord/CHANGELOG.md

.. not a general timeout.

Now, if a thread checks out a connection then dies, we can immediately
recover that connection and re-use it.

This should alleviate the pool exhaustion discussed in #12867. More
importantly, it entirely avoids the potential issues of the reaper
attempting to check whether connections are still active: as long as the
owning thread is alive, the connection is its business alone.

As a no-op reap is now trivial (only entails checking a thread status
per connection), we can also perform one in-line any time we decide to
sleep for a connection.

Only use BINARY for mysql case sensitive uniqueness check when column has a case insensitive collation.

Oops, I should had run the tests

When the adapter is with prepared statement disabled and the binds array
is not empty the connection adapter will try to set the binds values and
will fail. Now we are checking if the adapter has the prepared statement
disabled.

Fixes #12023

When mixing postgresql and another adapter like sqlite3 (for dev and test
respectively), the task `db:test:prepare` will fail due to the `enable_extension`
method not being defined in the abstract adapter. This patch simply adds an
empty definition to prevent it.

in favor of `begin_transaction`
with `:joinable` option.