More as_hal() methods

[JMS55]

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.

Description

• Change Texture::as_hal() callback to return a value, matching other as_hal callbacks
• Add TextureView::as_hal()
• Add CommandEncoder::as_hal_mut() (closes Allow hooking into command buffers on a backend-specific basis #3517)
• Add Adapter::texture_format_as_hal()

[codecov-commenter]

Codecov Report

Merging #3376 (d7dcc9b) into master (4400ff8) will increase coverage by 0.33%.
The diff coverage is 1.13%.

@@            Coverage Diff             @@
##           master    #3376      +/-   ##
==========================================
+ Coverage   64.64%   64.97%   +0.33%     
==========================================
  Files          86       86              
  Lines       42722    42890     +168     
==========================================
+ Hits        27616    27867     +251     
+ Misses      15106    15023      -83     

Impacted Files	Coverage Δ
wgpu-core/src/resource.rs	19.48% <0.00%> (-5.66%)	⬇️
wgpu-hal/src/dx11/adapter.rs	0.00% <0.00%> (ø)
wgpu-hal/src/dx11/mod.rs	0.00% <ø> (ø)
wgpu-hal/src/dx12/adapter.rs	80.34% <0.00%> (-1.05%)	⬇️
wgpu-hal/src/dx12/mod.rs	27.27% <ø> (ø)
wgpu-hal/src/empty.rs	0.00% <0.00%> (ø)
wgpu-hal/src/gles/adapter.rs	83.03% <0.00%> (-0.70%)	⬇️
wgpu-hal/src/gles/mod.rs	61.53% <ø> (ø)
wgpu-hal/src/lib.rs	26.92% <ø> (ø)
wgpu-hal/src/vulkan/adapter.rs	78.24% <0.00%> (-0.34%)	⬇️
... and 12 more

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[JMS55]

I've accidentally majorly screwed up this PR while trying to rebase :/. Going to delete this and try again...