Added new UNRESTRICTED_INDEX_BUFFER downlevel flag.

[Wumpf]

Checklist

• Run cargo clippy.
• Run RUSTFLAGS=--cfg=web_sys_unstable_apis cargo clippy --target wasm32-unknown-unknown if applicable.
• Add change to CHANGELOG.md. See simple instructions inside file.

Connections
n/a

Description

WebGL doesn't support buffers that are are used both as vertex and index buffer. This introduces a new downlevel feature to check for this.

Testing
Tested same application in browser and desktop (Metal). Browser now correctly logs an error:

panicked at 'wgpu error: Validation Error

Caused by:
    In Device::create_buffer
      note: label = `rerun logo`
    Downlevel flags BUFFER_USAGE_COMBINE_VERTEX_INDEX are required but not supported on the device.
This is not an invalid use of WebGPU: the underlying API or device does not support enough features to be a fully compliant implementation. A subset of the features can still be used. If you are running this program on native and not in a browser and wish to work around this issue, call Adapter::downlevel_properties or Device::downlevel_properties to get a listing of the features the current platform supports.

not super expressive but good enough I reckon

[cwfitzgerald]

The requirement is actually that index usage can only share with COPY_DST or COPY_SRC. INDEX | UNIFORM is also invalid. See https://registry.khronos.org/webgl/specs/latest/2.0/#BUFFER_OBJECT_BINDING.

There's also complexity where some buffer copies are invalid in webgl but this PR doesn't have to try to express that.

[cwfitzgerald]

Maybe MIXED_USAGE_INDEX_BUFFER or something.

[Wumpf]

Thanks for digging that up! Went ahead and looked into doing transfer restrictions as well which is why I called it UNRESTRICTED_INDEX_BUFFER

[codecov-commenter]

Codecov Report

Merging #3157 (484725f) into master (32febc5) will decrease coverage by 0.00%.
The diff coverage is 54.05%.

@@            Coverage Diff             @@
##           master    #3157      +/-   ##
==========================================
- Coverage   64.73%   64.73%   -0.01%     
==========================================
  Files          81       81              
  Lines       38737    38782      +45     
==========================================
+ Hits        25076    25105      +29     
- Misses      13661    13677      +16     

Impacted Files	Coverage Δ
wgpu-core/src/resource.rs	25.13% <ø> (ø)
wgpu-hal/src/dx11/adapter.rs	0.00% <0.00%> (ø)
wgpu-types/src/lib.rs	88.04% <0.00%> (-0.01%)	⬇️
wgpu-core/src/command/transfer.rs	69.92% <35.00%> (-0.85%)	⬇️
wgpu-core/src/device/mod.rs	66.37% <100.00%> (+0.06%)	⬆️
wgpu-hal/src/gles/adapter.rs	83.64% <100.00%> (+0.11%)	⬆️
wgpu/src/backend/direct.rs	55.25% <0.00%> (-0.65%)	⬇️
wgpu-hal/src/vulkan/adapter.rs	77.68% <0.00%> (-0.19%)	⬇️
wgpu-hal/src/dx12/adapter.rs	80.65% <0.00%> (-0.05%)	⬇️
wgpu/src/lib.rs	52.81% <0.00%> (ø)
... and 7 more

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