Fix SkBitSet.

Rename methods to be more like std::bitset and boost::dynamic_bitset.
Also fix findFirst to actually find the first and add tests.

Change-Id: Ic812c0a6d0ce1740c1cda900516f609ebbf5811c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/287676
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
9 files changed