op: Add 'srcFactor' and 'dstFactor' to the parameters in 'blending,clamping' test

[Gyuyoung]

This PR adds srcFactor and dstFactor to the parameters of 'blending,clamping' test in color_target_state.spec.ts.

Issue: #1835

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• 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.)

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• 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.

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[Gyuyoung]

When I applied these factors that include 'alpha', the test failed. Do you know any clue why?

[kainino0x]

If I run this PR without the filter then I hit an unreachable in calculateExpectedClampValue. But fixing that it still fails. At least some of the failures are because we expect the color and alpha channels to always be the same, but that's not always true: https://gpuweb.github.io/gpuweb/#enumdef-gpublendfactor

"src-alpha-saturated" (min(Asrc, 1 - Adst), min(Asrc, 1 - Adst), min(Asrc, 1 - Adst), 1)

Note the last channel has different factors.

The other issue I see is that when the format is rg16float, there is no alpha channel. Therefore dst-alpha won't have the initial value the code expects. I think missing channels default to ,0,0,1 so dst-alpha would be 1 (similar to this), but I'm not 100% sure about that.

[kainino0x]

It's ,0,0,1. Was confirmed in gpuweb/gpuweb#2025

[Gyuyoung]

The other issue I see is that when the format is rg16float, there is no alpha channel. Therefore dst-alpha won't have the initial value the code expects. I think missing channels default to ,0,0,1 so dst-alpha would be 1 (similar to this), but I'm not 100% sure about that.

yes, as you thought, the failures come from rg16float format and src-alpha-saturated factor. It's likely this PR should make the test use RGBA instead of using one value.

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