Add test for a glyph's signed top left values

Add test to highlight a bug handling the signed values
of the top left offset. Fix the bug by being careful with
sign extension.

Bug: skia:14163
Change-Id: I80e512fa9466cc54944af312ef53cba8c46ff4ca
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/659297
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Herb Derby <herb@google.com>
2 files changed