Migrate `SwitchCaseContainsExit` out of SkSLAnalysis.

This CL also removes `SwitchCaseFallsThrough` entirely; it was
not referenced anywhere.

Change-Id: I58298bf2a603615e37f4cced9db6d2f4c2c54d5a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/456473
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
4 files changed