swift

c056ca6f - Add PrunedLivenessBoundary mini-abstraction

Add PrunedLivenessBoundary mini-abstraction Simple wrapper to compute the boundary of PrunedLiveness. Pervasively useful utility for working with OSSA reference lifetimes and borrow scopes. This can also replace the implementation in CanonicalOSSALifetime. This will greatly simplify that utility's logic, preparing it to handle diagnostics (like move-only SILValue checking) and other features.