https://skia-review.googlesource.com/c/skia/+/451419 changed the meaning
of "offset" throughout SkSL, so that it was actually tracking line
numbers rather than offsets (and thus had a misleading name). This
completes the transition by renaming all of the now-misnamed "offset"
fields, parameters, and variables to "line'.
Bug: skia:12459
Change-Id: I394e6441f6ddfaad6d4098352ba9b1bfeaf273be
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/450644
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
58d47fa1ec