Improve constant folding for boolean vectors.

The additional tests from http://review.skia.org/441238 uncovered a gap
in the constant folder's abilities; it was not able to fold away
boolean vector comparisons even when they were constant. These are ES2
constant-expressions, so folding them properly is a requirement.

Change-Id: Ia0b4d5d1215c5fc2b247ac3f0dec4c8747d2153e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/441579
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
6 files changed