Implement getBVecComponent.

Like getIVecComponent or getFVecComponent, this retrieves the n'th
element of a Boolean compile-time constant vector. This will be used in
followup CLs.

Change-Id: Ib41c9c89cb773251e4c0d6cdcaea0437d8074e48
Bug: skia:11141
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/350918
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
4 files changed