From the Swift documentation:
"If you define an optional variable without providing a default value,
the variable is automatically set to nil for you."
We can express the same using the `isUniquelyReferencedNonObjC` API.
- Rename `isUniquelyReferencedNonObjC` to `isKnownUniquelyReferenced`.
- Cleanup `ManagedBufferPointer` by removing holdsUniqueOrPinnedReference` and
renaming `holdsUniqueReference` to `isUniqueReference`.
- No longer promise to return false from `isKnownUniquelyReferenced` for @objc
class instances.
SR-1962
rdar://21886410
All generic bridgeable types can bridge for all their instantiations now. Removing this ferrets out some now-unnecessary traps that check for unbridgeable parameter types.
Foundation provides a number of specific operators defined in the
global scope. Push all of these into their corresponding types. This
cleanup helps verify that the SE-0091 implementation is generally
functional.
