Blender Git Loki

PyAPI: unregister add-ons when exiting

This lets add-on authors avoid false positive leaks when exiting.
In particular GPUShaders's although it applies to any PyObject that
stores memory allocated by guarded-alloc.

While this does add overhead on exit, on my system it's
under 1/100th of a second with all addons enabled.

See: T71362