This CL add missing type conversions for f16, especially for SPIRV
backend which require special handling. A transform,
VectorizeMatrixConversions, are also added for SPIRV to replace a matrix
conversion to a matrix construction with converted column vectors.
Unittests for the transform and SPIRV writer, and end-to-end tests for
all conversion rules are added.
Bug: tint:1473, tint:1502, chromium:1356215
Change-Id: Iaff125e5dd295d35c4ab74757eb56b642802a51a
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/100483
Reviewed-by: David Neto <dneto@google.com>
Commit-Queue: Zhaoming Jiang <zhaoming.jiang@intel.com>
Kokoro: Kokoro <noreply+kokoro@google.com>