Rename GrAtlasTextBlob -> GrTextBlob

Change-Id: I61311b48f206890dfd1a20796d7d678cd05ef5a3
Reviewed-on: https://skia-review.googlesource.com/130140
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Herb Derby <herb@google.com>
12 files changed