Update association examples to Declarative API

Update association examples to Declarative API

### Description

Follows initial attempt in #10450 - but starts with simpler association examples.

### Checklist
This pull request is:

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

I was curious how to add these selectively to any of the type hint test suites, to prevent future drift, but didn't see anything too obvious.

Closes: #12031
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/12031
Pull-request-sha: dad6239370f23d52b4c0a1b21eba5752e216207e

Change-Id: Id5c2d65137c5e9d7e87778acd51b965c2bcf315a