This avoids a lot of confusion because the callers expect this type. Fixing it just required some redundancy and
bridging in the EnclosigValues implementation.
Key APIs necessary for using OSSA.
- BorrowingInstruction
- BeginBorrowValue
- scopeEndingOperands
- BorrowIntroducers
- EnclosingValues
- innerAdjacentPhis
These need to be complete to be correct.