Add caps bit for rewriting switch statements.

In early versions of GLSL, switch was not a supported statement, but it
can be emulated with a series of if statements inside a one-iteration
for loop.

Change-Id: I07ec88a5d0cae399828622791592e4a94e307586
Bug: skia:12450
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/452229
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
5 files changed