sokol_gfx.h resource bindings cleanup (issue #1037)

[floooh]

See: https://github.com/floooh/sokol/issues/1037

TODO:

• [x] rename sg_shader_desc.vertex_attrs back to attrs to be consistent with other sg_pipeline_desc
• [ ] consider removing the trailing _n from the new backend bind slots?
• [ ] update backends:
  • [x] Metal
  • [x] D3D11
  • [ ] GL
  • [ ] WebGPU
  • [ ] dummy
• [ ] fix sokol tests
• [x] fix raw samples
  • [x] Metal
  • [x] D3D11
  • [ ] GLFW
  • [ ] Emscripten
  • [ ] WebGPU
• update sokol-shdc:
  • [ ] auto-binding
  • [ ] manual bind slot definition via new meta-tags
• [ ] util headers:
  • [ ] sokol_imgui.h
  • [ ] sokol_gfx_imgui.h
  • [ ] sokol_gl.h
  • [ ] sokol_nuklear.h
  • [ ] sokol_debugtext.h
  • [ ] sokol_spine.h
  • [ ] sokol_fontstash.h
• [ ] fix language bindings samples:
  • [ ] zig
  • [ ] odin
  • [ ] nim
  • [ ] rust
  • [ ] d
  • [ ] jai
• [ ] fix other projects
  • [ ] doom
  • [ ] v6502r
  • [ ] chips
  • [ ] qoiview
  • [ ] cimgui-starter-kit
  • [ ] ...