Notes:
- Separates ChainedStruct to be reusable without cpp header. (Also
updates native structs to directly use it.)
- Manually implements the descriptor in DawnNative.
- Reworks ChainUtils with mapping from struct to STypes.
- Updates the tests to use either SetPlatformForTesting which is still
required because DawnTest uses a "global" instance for all tests and
some tests require setting (and cleaning up) a test specific platform.
Bug: dawn:1374
Change-Id: I078c78f22c5137030cf3cf0e8358fe4373ee9c6c
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/132268
Reviewed-by: Austin Eng <enga@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Loko Kung <lokokung@google.com>
14ed533565