For consistency with https://github.com/rails/rails/pull/15557

The contract of `_field_changed?` assumes that the old value is always
type cast. That is not the case for the value in `Column#default` as
things are today. It appears there are other public methods that
assume that `Column#default` is type cast, as well. The reason for this
change originally was because the value gets put into `@raw_attributes`
in initialize. This reverts to the old behavior on `Column`, and updates
`initialize` to make sure that the values are in the right format.

Many of the methods defined in `AttributeMethods::Serialization` can be
refactored onto this type as well, but this is a reasonable small step.
Removes the `Type` class, and the need for `decorate_columns` to handle
serialized types.

- Create a consistent API across adapters for building new columns
- Use it for custom properties so we don't get `UndefinedMethodError`s
  in stuff I'm implementing elsewhere.

Working towards re-implementing serialized attributes to use the
properties API exposed the need for this, as serializing a column
shouldn't change the order of the columns.

`ActiveRecord::ConnectionAdapters::Type::Value` =>
`ActiveRecord::Type::Value`

Making this part of the public API was premature, let's make it private
again while I continue to work on the surrounding code.

With ActiveRecord::Properties, we now have a reasonable path for users
to continue to keep this behavior if they want it. This is an edge case
that has added a lot of complexity to the code base.

As a result of all of the refactoring that's been done, it's now
possible for us to define a public API to allow users to specify
behavior. This is an initial implementation so that I can work off of it
in smaller pieces for additional features/refactorings.

The current behavior will continue to stay the same, though I'd like to
refactor towards the automatic schema detection being built off of this
API, and add the ability to opt out of automatic schema detection.

Use cases:

- We can deprecate a lot of the edge cases around types, now that there
  is an alternate path for users who wish to maintain the same behavior.
- I intend to refactor serialized columns to be built on top of this
  API.
- Gem and library maintainers are able to interact with `ActiveRecord`
  at a slightly lower level in a more stable way.
- Interesting ability to reverse the work flow of adding to the schema.
  Model can become the single source of truth for the structure. We can
  compare that to what the database says the schema is, diff them, and
  generate a migration.