Standalone animation player has inconsistent GPU context activation
paradigm compared with standard rendering paths. The Metal backend
utilises the context activation step to refresh target window swapchains
from within the GHOST module.
This PR adds activation and deactivation calls, and also aims to clean up
GPU_render_begin/end setup to ensure all paths are covered.
Also resolves a bug upon shutdown wherein GPU resources which may
be tied to a GPU context are released during IMB_exit(), which is called
after GPU context destruction.
Authored by Apple: Michael Parkin-White
Pull Request: https://projects.blender.org/blender/blender/pulls/114573
05c56603a9