Finish uniform support for SkMesh.

SkMesh now takes SkData that contains the uniform values.

Change-Id: I286e7559ba692ce15925a54f59c2e829b6b5448f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/546096
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
7 files changed