[Draft] sokol_gfx.h: introduce separate sampler objects

[floooh]

Add separate sampler objects, some additional renaming (more in line with WebGPU conventions).

TODO:

• [x] fix sokol-spine trying to stash an image- and sampler-id into the render_object pointer => probably need to heap allocate an image-sampler-pair struct and use the render_object to point there...
• [x] fix sokol-shdc tests
• [x] don't allow to override the sampler object in sokol_imgui.h (because ImTextureID is 32-bits on WASM)
• [x] don't allow to override the sampler object in sokol_nuklear.h (because nk_handle is 32-bits on WASM)
• [x] fix iOS Metal backend errors
• [x] extend Windows GL loader with new sampler functions
• [x] fix dummy backend
• [x] extend sokol-gfx tests for sampler objects
• [x] fix all the other tests (sokol-spine etc)
• [x] allow depth-only rendering:
  • [x] _sg_validate_pass_desc()
  • [x] sg_make_pipeline() => .colors[0].pixel_format = SG_PIXELFORMAT_NONE
  • [x] _sg_mtl_create_pipeline()
  • [x] _sg_gl_create_pipeline()
  • [x] _sg_d3d11_create_pipeline()
  • [x] _sg_mtl_create_pass()
  • [x] _sg_gl_create_pass()
  • [x] _sg_d3d11_create_pass()
  • [x] sg_begin_pass() => don't take width/height from first color attachment
  • [x] _sg_mtl_begin_pass()
  • [x] _sg_gl_begin_pass()
  • [x] _sg_d3d11_begin_pass()
• [ ] new sample which samples depth texture with a comparison sampler
  • [x] macOS/Metal
  • [x] macOS/GL
  • [x] iOS/Metal
  • [ ] iOS/GL (something unrelated seems to be broken currently with iOS/GL on the simulator)
  • [x] Windows/D3D11
  • [x] Windows/GL
  • [x] Linux/GL
  • [x] Linux/GLES3
  • [x] Android/GLES3
  • [x] Emscripten/GLES3
• [ ] ~~new sample which fetches samples from an MSAA texture (???)~~ (won't work on the GL backend anyway, better to wait with this after the WebGPU backend is finished)
• [ ] doc updates:
  • [ ] sokol_gfx.h
  • [ ] sokol-shdc
  • [x] sokol_gl.h
  • [x] ~~sokol_debugtext.h~~ (no public API changes)
  • [x] ~~sokol_fontstash.h~~ (no public API changes)
  • [x] sokol_spine.h
  • [x] sokol_imgui.h
  • [x] sokol_nuklear.h
  • [x] sokol_shape.h
  • [x] sokol_gfx_imgui.h
• [x] fix util headers (except hlsl shaders):
  • [x] sokol_debugtext.h
  • [x] sokol_fontstash.h
  • [x] sokol_gl.h
  • [x] sokol_imgui.h
  • [x] sokol_nuklear.h
  • [x] sokol_spine.h
  • [x] sokol_shape.h
  • [x] sokol_gfx_imgui.h
• [x] update hlsl shaders in:
  • [x] sokol_debugtext.h
  • [x] sokol_fontstash.h
  • [x] sokol_gl.h
  • [x] sokol_imgui.h
  • [x] sokol_nuklear.h
  • [x] sokol_spine.h
• [x] fix samples:
  • [x] d3d11
  • [x] glfw
  • [x] html5
  • [x] metal
  • [x] sapp
• [x] fix sokol-shdc backends:
  • [x] zig
  • [x] odin
  • [x] nim
  • [x] rust
  • [x] bare
  • [x] ...?
• [x] fix language bindings (also special case names):
  • [x] sokol-zig
  • [x] sokol-odin
  • [x] sokol-nim
  • [x] sokol-rust
• [x] fix language bindings samples:
  • [x] sokol-zig
  • [x] sokol-odin
  • [x] sokol-nim
  • [x] sokol-rust

What's new:

• Fix: sg_begin_pass() would use the wrong attachment width/height if rendering to a mip level
• Metal backend now checks for shared vs managed resources support on macOS
• Metal backend now supports clamp-to-border-color on iOS devices if possible (depends on iOS version and GPU family)
• new sg_desc.mtl_force_managed_storage_mode config boolean to force managed storage mode on macOS devices (mainly useful for debugging)
• new funcs:
  • sg_make_sampler()
  • sg_destroy_sampler()
  • sg_init_sampler()
  • sg_uninit_sampler()
  • sg_alloc_sampler()
  • sg_dealloc_sampler()
  • sg_fail_sampler()
• removed sampler state in sg_image_desc:
  • .min_filter
  • .mag_filter
  • .wrap_u
  • .wrap_v
  • .wrap_w
  • .border_color
  • .max_anisotropy
  • .min_lod
  • .max_lod
• sg_filter reduced to: none, nearest, linear
• new struct: sg_sampler_desc: sampler state moved over from sg_image_desc, plus:
  • .mipmap_filter
  • .compare
• additional reflection state and some general cleanup in sg_shader_desc (requires new sokol-shdc version):
  • new: sg_shader_image_desc.used
  • new: sg_shader_image_desc.multisampled
  • new: sg_sampler_type renamed to sg_image_sample_type
  • removed: sg_shader_image_desc.name
  • new struct: sg_shader_sampler_desc
  • repurposed enum sg_sampler_type (sample vs compare)
  • new struct: sg_shader_image_sampler_pair_desc
• fix sokol-shdc so that it's possible to use textureSize()
• sg_bindings:
  • changed: .vs_images[] => .vs.images[]
  • changed: .fs_images[] => .fs.images[]
  • new: .vs.samplers[]
  • new: .fs.samplers[]
• renamed some types related to sg_pipeline_desc:
  • sg_buffer_layout_desc => sg_vertex_buffer_layout_state
  • sg_vertex_attr_desc => sg_vertex_attr_state
  • sg_layout_desc => sg_vertex_layout_state
• related fixes in
  • sokol_debugtext.h (only shaders)
  • sokol_fontstash.h (only shaders)
  • sokol_gl.h (shaders, and sgl_texture() now takes sg_image + sg_sampler)
  • sokol_imgui.h (shaders, new helper function simgui_imtextureid() to create ImTextureID handle from sg_image and sg_sampler)
  • sokol_nuklear.h (shader, snk_nkhandle() helper function to wrap sg_image+sg_sampler in nk_handle => use nk_image_handle(snk_nkhandle(img, smp)) to create a Nuklear image handle!
  • sokol_shapes.h rename some functions to match sokol_gfx.h struct renamings
  • sokol_spine.h: (shaders, user needs to create sampler via sg_init_sampler() (similar to sg_init_image))
  • sokol_gfx.h: remove err_ trace hook functions (redundant with new error logging)