macOS Rework Umbrella

This is an umbrella issue to keep track of the macOS Rework PRs and outstanding issues.

Pull Requests

Each phase depends on the previous phase's pull requests.

Phase 1

Pull Request	Description
#32161 - Initial	Closes #31770 Closes #31813 Closes #31875 Closes #31933

Phase 2

Pull Request	Description
#32361 - App Icon	Closes #31895
#32362 - Button Release	Closes #31899
#32363 - Event Loop	Closes #30419
#32364 - Subplot Tool	Native subplot tool. Closes #27592
Pending - Timer	Mimic QTimer. Helps with #29029 and #29062
#32365 - Toolbar	Cosmetic changes to toolbar buttons.

Phase 3

Pull Request	Description
Pending - Threading	Closes #31968. Fixes issues on free-threaded build.

Remaining Issues (no PR planned yet)

#32041 - This involves a simple compatibility shim, deprecation warning, and notifying other projects. Likely not applicable if we keep "macosx" in 3.12 and deprecate the whole backend.

Remaining work without issues or PRs:

• Research IPython and the mapping between "macosx"/"macos"/"osx" in _fix_ipython_backend2gui.
• "test_backend_macosx.py" should probably become "test_backend_macos.py", and a new "test_backend_macosx.py" goes in to test deprecation notices and/or the compatibility shim.
• Only install PyOS_InputHook when we also install our app delegate (see #32314). Add API to manually install our input hook, if desired. Adjust app delegate instantiation - should it only occur if we enter _macos__init with no NSApp?
• Documentation changes / API Notes / Release Notes
• Change "GUI: MacOSX" label to "GUI: macOS". Update labeler.yml
• Actual switchover from macosx to macos as default