Rename GrAtlasTextBatch files to GrAtlasTextOp

Change-Id: I3ce7321577c236a95811d7a2da798d4eb2e0cbd3
Reviewed-on: https://skia-review.googlesource.com/6116
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
5 files changed