Remove ErrorReporter pointer from DSL

This centralizes the ownership of the current ErrorReporter solely in
SkSLContext.

Change-Id: I3fdffb8133e9800ef9b898a62c2d418560079b83
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/441237
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
5 files changed