Document and improve extension detection

[teoxoy]

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

Description
We used to require VK_EXT_sampler_filter_minmax and never used it.
We used to require VK_KHR_maintenance2 and VK_KHR_timeline_semaphore unconditionally.
We never required VK_EXT_image_robustness and VK_EXT_robustness2 (if available).
We weren't building PhysicalDeviceDescriptorIndexingFeaturesEXT for Vulkan 1.2+.
We weren't building GetPhysicalDeviceProperties2 for Vulkan 1.0, this in turn making some features unusable.

Testing

[codecov-commenter]

Codecov Report

Merging #3327 (e54ae89) into master (aa46e82) will increase coverage by 0.99%.
The diff coverage is 47.88%.

❗ Current head e54ae89 differs from pull request most recent head 1e966d8. Consider uploading reports for the commit 1e966d8 to get more accurate results

@@            Coverage Diff             @@
##           master    #3327      +/-   ##
==========================================
+ Coverage   64.10%   65.09%   +0.99%     
==========================================
  Files          86       86              
  Lines       42591    42874     +283     
==========================================
+ Hits        27301    27910     +609     
+ Misses      15290    14964     -326     

Impacted Files	Coverage Δ
wgpu-hal/src/vulkan/adapter.rs	78.49% <36.53%> (+2.05%)	⬆️
wgpu-hal/src/vulkan/instance.rs	38.40% <78.94%> (+0.80%)	⬆️
wgpu-core/src/hub.rs	60.67% <0.00%> (-0.31%)	⬇️
wgpu-hal/src/dx12/mod.rs	27.27% <0.00%> (ø)
wgpu-hal/src/vulkan/mod.rs	56.37% <0.00%> (ø)
wgpu-hal/src/dx12/command.rs	73.46% <0.00%> (+0.02%)	⬆️
wgpu-core/src/device/mod.rs	66.82% <0.00%> (+0.09%)	⬆️
wgpu-core/src/validation.rs	59.01% <0.00%> (+0.13%)	⬆️
wgpu-hal/src/auxil/dxgi/conv.rs	76.02% <0.00%> (+0.33%)	⬆️
... and 15 more

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[cwfitzgerald]

Works on my machine - g2g after nit