[func-sig-opts] Add a new mangling for the guaranteed->owned transformation.

I followed the example of the owned->guaranteed transformation.

rdar://38196046

include/swift/Demangling/Demangle.h

@@ -94,6 +94,7 @@ enum class FunctionSigSpecializationParamKind : unsigned {
   Dead = 1 << 6,
   OwnedToGuaranteed = 1 << 7,
   SROA = 1 << 8,
+  GuaranteedToOwned = 1 << 9,
 };
 
 /// The pass that caused the specialization to occur. We use this to make sure