Move (re)generation of the GrTextBlob from GrTextContext to the blob

This resolves many scoping issues, which complicate this code.

Change-Id: Ib0d283d95ff8a563176a333c8d388947650df4d2
Reviewed-on: https://skia-review.googlesource.com/c/169761
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Herb Derby <herb@google.com>
7 files changed