[skottie] Add support for explicit text line breaks

To support wacky explicit AE line breaking:

  * add sksg::TextBlob (SG node backed by externally-built text blobs)
  * add skottie::TextAdapter logic to handle \r line breaks and construct
    the blob explicitly

Change-Id: I2eed9adf28a8c3c1f7de5bbec3d32abd7ddbd484
Reviewed-on: https://skia-review.googlesource.com/c/167384
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
4 files changed