Font feature start/end indexes must be relative to the start of the utf8
buffer passed to SkShaper. SkParagraph had been passing indexes based on
the start of the block.
See https://github.com/flutter/flutter/issues/103615
Change-Id: Ie15611cb05e3532fc34d66724ac347b9bddc3c8c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/540157
Reviewed-by: Julia Lavrova <jlavrova@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Jason Simmons <jsimmons@google.com>
4220ffbaf2