[ownership] Add some helpers to BorrowedValue that lets you use it easily as a value.

Specifically I provided a '->' and a '*' operator. So now you can do:

```
borrowedValue->callSILValueMethod();
```

and explicitly cast to SILValue using '*'.

Author: gottesmm

include/swift/SIL/OwnershipUtils.h

@@ -468,6 +468,13 @@ struct BorrowedValue {
     return foundAnyReborrows;
   }
 
+  // Helpers to allow a BorrowedValue to easily be used as a SILValue
+  // programatically.
+  SILValue operator->() { return value; }
+  SILValue operator->() const { return value; }
+  SILValue operator*() { return value; }
+  SILValue operator*() const { return value; }
+
 private:
   /// Internal constructor for failable static constructor. Please do not expand
   /// its usage since it assumes the code passed in is well formed.