Adds a first-pass version of vertex pulling. This is missing several important things such as buffer offsets, support for more types, and clamping.
Bug: dawn:480, tint:206
Change-Id: Ia8a3abc446bca4c5a40e064f85fb59de1c3f5af9
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/26260
Reviewed-by: dan sinclair <dsinclair@chromium.org>
Commit-Queue: dan sinclair <dsinclair@chromium.org>