Deprecate session.execute(query) usage

[CaselIT]

Currently this somewhat works but it's not tested anywhere so it may have subtle edge cases

See also #11118

[jvanasco]

The pattern of Session.execute(query) appears in a handful of tests, including:

• https://github.com/sqlalchemy/sqlalchemy/blob/main/test/orm/inheritance/test_polymorphic_rel.py#L328

• https://github.com/sqlalchemy/sqlalchemy/blob/main/test/orm/test_eager_relations.py#L740

• https://github.com/sqlalchemy/sqlalchemy/blob/main/test/orm/test_froms.py#L855

• https://github.com/sqlalchemy/sqlalchemy/blob/main/test/orm/test_query.py - 11 instances

There are more tests of Connection.execute(q), but the Session.execute(q) pattern does appear in more than a dozen tests.