use new llvm::Optional API

`getValue` -> `value`
`getValueOr` -> `value_or`
`hasValue` -> `has_value`
`map` -> `transform`

The old API will be deprecated in the rebranch.
To avoid merge conflicts, use the new API already in the main branch.

rdar://102362022

lib/SILOptimizer/Analysis/MemoryBehavior.cpp

@@ -93,7 +93,7 @@ public:
       cachedIsLetValue =
           V->getType().isAddress() && isLetAddress(getValueAddress());
     }
-    return cachedIsLetValue.getValue();
+    return cachedIsLetValue.value();
   }
 
   // Return true is the given address (or pointer) may alias with 'V'.