Adds CTS test coverage for the `snorm10-10-10-2` vertex format. (#4695)

* This PR adds CTS test coverage for the `snorm10-10-10-2` vertex format.

* Adds `snorm10-10-10-2` to `kVertexFormatInfo` in `capability_info.ts` (with an explicit cast until `@webgpu/types` is updated).
* Adds signed 10-10-10-2 bit-packing (`makeRgb10a2Signed`) and normalization (`normalizeRgb10a2Signed`) test helpers.
* Adds packed format test data in `correctness.spec.ts` to verify conversion from raw vertex data to `vec4<f32>` in the vertex shader.

Issue: https://github.com/gpuweb/gpuweb/issues/6292

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**Requirements for PR author:**

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

**Requirements for [reviewer sign-off](https://github.com/gpuweb/cts/blob/main/docs/reviews.md):**

- [ ] Tests are properly located.
- [ ] [Test descriptions](https://github.com/gpuweb/cts/blob/main/docs/intro/plans.md) are accurate and complete.
- [ ] Tests provide complete coverage (including validation control cases). **Missing coverage MUST be covered by TODOs.**
- [ ] Tests avoid [over-parameterization](https://github.com/gpuweb/cts/blob/main/docs/organization.md#parameterization) (see case count report).

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

* Roll @webgpu/types to 0.1.72

* Address review comments on makeRgb10a2Signed

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Co-authored-by: Kai Ninomiya <kainino@chromium.org>