Metal Backend: Add fallback for Add-ons that use BGL or Incorrect shader-code with GPU module. #103863

In order to make metal default for blender it should not crash when add-ons are enabled that use the BGL module or has shaders that don't compile on Metal.
The idea as discussed is to have a fallback opengl context around where GL calls can be passed to, so it doesn't fail when Metal backend isn't supported. This fallback won't draw/read from the screen, it only makes sure that Blender doesn't crash. Perhaps in stead of an OpenGL context we could create a dummy context where unsupported calls will land.

Looking at how BGL accesses OpenGL we could modify the BGL_Wrap to do nothing when Metal is the active backend.

See release/scripts/addons/measureit/measureit_render.py.

buffer = bgl.Buffer(bgl.GL_BYTE, width * height * 4)
        bgl.glReadBuffer(bgl.GL_COLOR_ATTACHMENT0)
        bgl.glReadPixels(0, 0, width, height, bgl.GL_RGBA, bgl.GL_UNSIGNED_BYTE, buffer)```

In the case shaders cannot compile the metal backend will set a flag that will control an error message to be displayed to the user.

Added subscribers: @Jeroen-Bakker, @Michael-Parkin-White-Apple

Changed status from 'Needs Triage' to: 'Confirmed'

Added subscriber: @PratikPB2123

Added subscriber: @mycoconut

This issue was referenced by cac6b6f388

Added subscriber: @Alaska

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Metal Backend: Add fallback for Add-ons that use BGL or Incorrect shader-code with GPU module. #103863