[sil] Make SILType::getCategoryType() use getRawASTType() instead of getASTType().

The reason why this makes sense is that this method is attempting to return the
current SILType but with a different category. So using getASTType() here and by
mistake removing move only would break semantics. Additionally, not making this
change breaks the expectation that this API would be idempotent.

Author: gottesmm

include/swift/SIL/SILType.h

@@ -151,7 +151,7 @@ class SILType {
 
   /// Returns the \p Category variant of this type.
   SILType getCategoryType(SILValueCategory Category) const {
-    return SILType(getASTType(), Category);
+    return SILType(getRawASTType(), Category);
   }
 
   /// Returns the variant of this type that matches \p Ty.getCategory()