Texture compression unaligned

[castano]

Issue: gpuweb/gpuweb#2006

Add tests to support the proposed 'texture-compression-unaligned' feature. gpuweb/gpuweb#6312

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Requirements for PR author:

• All missing test coverage is tracked with "TODO" or .unimplemented().
• New helpers are /** documented */ and new helper files are found in helper_index.txt.
• Test behaves as expected in a WebGPU implementation. (If not passing, explain above.)
• Test have be tested with compatibility mode validation enabled and behave as expected. (If not passing, explain above.)

Requirements for reviewer sign-off:

• Tests are properly located.
• Test descriptions are accurate and complete.
• Tests provide complete coverage (including validation control cases). Missing coverage MUST be covered by TODOs.
• Tests avoid over-parameterization (see case count report).

When landing this PR, be sure to make any necessary issue status updates.

[github-actions]

Results for build job (at d95bffb):

-webgpu:api,operation,adapter,requestDevice:features,known:* - 24 cases, 24 subcases (~1/case)
+webgpu:api,operation,adapter,requestDevice:features,known:* - 25 cases, 25 subcases (~1/case)
+webgpu:api,operation,command_buffer,copyTextureToTexture:color_textures,compressed,unaligned,non_array:* - 94 cases, 1974 subcases (~21/case)
+webgpu:api,operation,command_buffer,image_copy:compressed_textures,unaligned_mip_level_0:* - 156 cases, 780 subcases (~5/case)
+webgpu:api,validation,capability_checks,features,texture_compression_unaligned:createTexture,unaligned_size:* - 416 cases, 416 subcases (~1/case)
-TOTAL: 283186 cases, 2326094 subcases
+TOTAL: 283853 cases, 2329265 subcases