Add tests for validation that stripIndexFormat and indexFormat must m…

[Kangz]

…atch

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 62222b3):

+webgpu:api,validation,encoding,cmds,render,draw:index_buffer_format:* - 1 cases, 36 subcases (~36/case)
+webgpu:api,validation,encoding,cmds,render,draw:index_buffer_format_dirtying:* - 1 cases, 6 subcases (~6/case)
-TOTAL: 281247 cases, 2322858 subcases
+TOTAL: 281249 cases, 2322900 subcases

[toji]

LGTM, thanks!