Test CopyEI2T and GPUExternalTexture convert video contents to display-p3 color space

[shaoboyan]

This PR refactor video related utils and add tests to cover GPUExternalTextureDescriptor:colorSpace = 'display-p3'.

Issue: #2362

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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.)

Requirements for reviewer sign-off:

• Tests are properly located in the test tree.
• Test descriptions allow a reader to "read only the test plans and evaluate coverage completeness", and accurately reflect the test code.
• Tests provide complete coverage (including validation control cases). Missing coverage MUST be covered by TODOs.
• Helpers and types promote readability and maintainability.

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

[shaoboyan]

NOTE: this PR catches implemenation issues in chromium:

• GPUExternalTexture handles crop+rotate video not correctly.
• GPUExternalTexture in compute pipeline has big diff with expectation while render pipeline not (Due to case error)
• display-p3 is not supported (fail a check) in chromium.

[kainino0x]

Filled in issue #2362 above

[shaoboyan]

Almost forget to upload the excel
Display-P3.xlsx
Will detailed the steps in docs/

[kainino0x]

Good fix, I didn't realize this was mutating in place ^_^ We should make this take a readonly input.

I think you meant to remove these lines as well.

I will fix both.

[kainino0x]

Ugh, sadly web_platform/util.ts is a place where readonly types don't get enforced. Oh well, at least it would have caught these lines.

[shaoboyan]

Thanks for the fix!