Complement type annotations for ARRAY

Complement type annotations for ARRAY

This complements the type annotations of the `ARRAY` class, in preparation of #12384.

This pull request is:

- [ ] A documentation / typographical / small typing error fix
	- Good to go, no issue or tests are needed
- [ ] 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.
- [x] 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.

Related to https://github.com/sqlalchemy/sqlalchemy/issues/6810

Closes: #12386
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/12386
Pull-request-sha: c9513ce729fa1116b46b02336d4e2cda3d096fee

Change-Id: If9df4708c8e597eedc79ee3990792fa6c72f1afe
(cherry picked from commit 0bf7e02afbec557eb3a5607db407f27deb7aac77)