Support Python 3.10a5 or 3.9x with support explicitly enabled.
- Enable Python's postponed annotations for Blender's RNA classes
types registered on startup.
- Using postponed annotations has implications for how they are defined,
since they must evaluate in the modules name-space instead of the
classes name-space. See changes to annotations in `release/scripts`.
- Use `from __future__ import annotations` at the top of the module
to ensure the script will run with Python 3.10.
- Old logic is kept since it could be used if PEP-649 is supported.
Resolves T83626
Ref D10474
08dbc4f996