Check clearing of 3d textures when rendering to a slice

[greggman]

There was an issue in some browsers where, when rendering to a slice of a 3d texture, they'd mark the entire texture as initialized even though only the individual slice was initialized.

Updated the tests so they check the entire texture. Also updated them to try every format.

Several formats are failing in Chrome even with the latest updated to address this.

Issue: #

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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 1451f21):

-webgpu:api,operation,rendering,3d_texture_slices:one_color_attachment,mip_levels:* - 6 cases, 6 subcases (~1/case)
-webgpu:api,operation,rendering,3d_texture_slices:multiple_color_attachments,same_mip_level:* - 2 cases, 8 subcases (~4/case)
-webgpu:api,operation,rendering,3d_texture_slices:multiple_color_attachments,same_slice_with_diff_mip_levels:* - 2 cases, 2 subcases (~1/case)
+webgpu:api,operation,rendering,3d_texture_slices:one_color_attachment,mip_levels:* - 234 cases, 234 subcases (~1/case)
+webgpu:api,operation,rendering,3d_texture_slices:multiple_color_attachments,same_mip_level:* - 78 cases, 312 subcases (~4/case)
+webgpu:api,operation,rendering,3d_texture_slices:multiple_color_attachments,same_slice_with_diff_mip_levels:* - 78 cases, 78 subcases (~1/case)
-TOTAL: 280796 cases, 2322135 subcases
+TOTAL: 281176 cases, 2322743 subcases

[kainino0x]

apologies for delay, I got a huge amount of reviews at once on wednesday and this one was a bit hard to read (I still didn't read it super closely but I found the core logic and it looks good)