Metal: Ensure correct output texture format selection

[stuartcarnie]

Ensure the correct output texture format is selected when creating the MetalFX Spatial Shader context.

before	after

Note

Also verified with tps-demo and @Calinou's additions to allow selecting MetalFX upscalers.

[stuartcarnie]

I have an addition to this PR, as it doesn't handle toggling the viewport from HDR to SDR.

[stuartcarnie]

@clayjohn I added a call to _configure_3d_render_buffers(viewport); when the viewport is toggled from SDR to HDR, to allow internal buffers to be recreated, which allows the spatial shader to update its descriptor to match the updated output format:

CleanShot.2025-08-08.at.12.52.57.mp4

[bruvzg]

I can reproduce the issue and confirm it is fixed. Tested on M4 Pro, macOS 15.6 (24G84).

[Calinou]

Code looks good to me.

[Repiteo]

Thanks!