typing: pg: type NamedType create/drops (fixes #12557)

typing: pg: type NamedType create/drops (fixes #12557)

Type the `create` and `drop` functions for `NamedType`s

Also partially type the SchemaType create/drop functions more generally

One change to this is that the default parameter of `None` is removed. It doesn't work and will fail with a `AttributeError` at runtime since it immediately tries to access a property of `None` which doesn't exist.

Fixes #12557

This pull request is:

- [X] A documentation / typographical / small typing error fix
	- Good to go, no issue or tests are needed
- [X] A short code fix
	- please include the issue number, and create an issue if none exists, which
	  must include a complete example of the issue.  one line code fixes without an
	  issue and demonstration will not be accepted.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.   one line code fixes without tests will not be accepted.
- [ ] A new feature implementation
	- please include the issue number, and create an issue if none exists, which must
	  include a complete example of how the feature would look.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.

**Have a nice day!**

Closes: #12558
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/12558
Pull-request-sha: 75c8d81bfb68f45299a9448d45dda446532205d3

Change-Id: I173771d365f34f54ab474b9661e1cdc70cc4de84