[ConstraintSystem] Look through ArgumentAttribute element when computing a callee

This element is used purely for diagnostic purposes and locator
should behavior as if it's completely transparent.

(cherry picked from commit 622475bf15)

lib/Sema/ConstraintSystem.cpp

@@ -730,7 +730,9 @@ ConstraintLocator *ConstraintSystem::getCalleeLocator(
   }
 
   if (locator->isLastElement<LocatorPathElt::ArgumentAttribute>()) {
-    return getConstraintLocator(anchor, path.drop_back());
+    auto argLoc = getConstraintLocator(anchor, path.drop_back());
+    return getCalleeLocator(argLoc, lookThroughApply, getType, simplifyType,
+                            getOverloadFor);
   }
 
   // If we have a locator that starts with a key path component element, we