Implement queue.copy_external_image_to_texture for WebGL2 and improve WebGPU Impl

[cwfitzgerald]

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.

Still todo:

• Merge Fill out tex*Image*D overloads for WebGL2 grovesNL/glow#234
• Add tests

Connections

Closes #1888.

Follows up on #2781.

Description

Implements copy_external_image_to_texture fully on both WebGPU and WebGL - including all 4 different types that are supported by WebGPU.

Testing

Testing todo.

[codecov-commenter]

Codecov Report

Merging #3288 (3886b8b) into master (c1a0912) will decrease coverage by 0.07%.
The diff coverage is 17.56%.

@@            Coverage Diff             @@
##           master    #3288      +/-   ##
==========================================
- Coverage   64.50%   64.42%   -0.08%     
==========================================
  Files          86       86              
  Lines       42691    42776      +85     
==========================================
+ Hits        27536    27558      +22     
- Misses      15155    15218      +63     

Impacted Files	Coverage Δ
wgpu-core/src/conv.rs	92.42% <0.00%> (-4.41%)	⬇️
wgpu-core/src/device/queue.rs	70.33% <ø> (+0.14%)	⬆️
wgpu-hal/src/dx11/adapter.rs	0.00% <0.00%> (ø)
wgpu-hal/src/empty.rs	0.00% <ø> (ø)
wgpu-hal/src/gles/command.rs	72.13% <ø> (ø)
wgpu-hal/src/gles/mod.rs	61.53% <ø> (ø)
wgpu-hal/src/gles/queue.rs	61.31% <ø> (ø)
wgpu-hal/src/lib.rs	26.92% <ø> (ø)
wgpu-types/src/lib.rs	86.01% <0.00%> (-2.06%)	⬇️
wgpu/src/backend/direct.rs	56.59% <0.00%> (-0.28%)	⬇️
... and 13 more

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[teoxoy]

Have a few comments, otherwise it looks good!

[teoxoy]

Good stuff!