Use SkSL "offset" to actually mean "line"

SkSL internally tracks token offsets, but only ever reports errors using
line numbers. With the introduction of the DSL, which (being embedded in
C++ source) only has access to line numbers in the first place, tracking
offsets went from merely providing little benefit to actively making
life more difficult.

We are changing SkSL's position tracking from handling offsets to
handling line numbers, but to simplify the review process the change is
split up into two main steps. The first step (this CL) starts using
line numbers everywhere, but avoids the thousand-line churn of actually
renaming "offset", so most "offset" fields, variables, and parameters
will be briefly misnamed and will actually contain a line number.

The followup CL will complete the process by renaming all of the
now-misnamed fields, variables, and parameters, but will not make any
behavioral changes.

Bug: skia:12459
Change-Id: I30dc87cf4b816c5ddd7b8ae1be32586388962085
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/451419
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
17 files changed