[skottie] Compute tight bounds in skottie::Shaper

Instead of relying on conservative text blob bounds, update
Shaper::Result::computeBounds() to be more accurate.

Also add a skottie::Shaper unit test.

Change-Id: Icf17afcc814329197825e8d404416b6b7060c79d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/204480
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
2 files changed