Blocks #597

d3d12 samples that depend on samples/common were created before zgui/zmath and can be refactored:
#559 (comment)

samples/common holds the csGenerateMipmaps in common.hsl, which belongs in zd3d12 alongside zd3d12.MipmapGenerator.

FrameStats should be moved to zd3d12.GraphicsContext to reach parity with zgpu.GraphicsContext

The following depend on samples/common:

1. samples\audio_experiments
2. samples\audio_playback_test
3. samples\bindless
4. samples\directml_convolution_test
5. samples\mesh_shader_test
6. samples\rasterization
7. samples\simple_raytracer
8. samples\textured_quad
9. samples\triangle
10. samples\vector_graphics_test
11. samples\simple_openvr (common.hlsl only)