Make GrAtlasTextOp a non-legacy GrMeshDrawOp

Change-Id: Ib9eaf149100b0ccecf1c18a755263f2579b8e6f6
Reviewed-on: https://skia-review.googlesource.com/23482
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
9 files changed