Implement boolean short circuit folding in SkSL

Bug: skia:
Change-Id: I0bb0506bbe6973c004ced22648588d82d2bac497
Reviewed-on: https://skia-review.googlesource.com/151820
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
2 files changed