Support multiple extensions with different Python versions in a similar
way to how "platforms" are handled now.
This will be needed when Blender upgrades to a newer version of Python
so extensions which have a binary dependency on Python 3.11 don't
attempt to install in a Blender built with a newer Python version.
Details:
- Extensions from incompatible Python versions are not listed.
- Python versions are extracted from wheel names.
- An extension may include wheels for multiple Python versions,
only the compatible wheels will be installed.
- Links may include a "python_versions" field which is checked
when dropping into Blender.
- JSON generated by the "server-generate" command include the:
"python_versions" field for extensions that include wheels.
- The "python_versions" field is optional, when omitted no version
checks are performed.
Also correct watch_test make target.
Ref #128750.
a3a3dda563