[CSFix] Extend locator with ArgumentAttribute for escaping/inout fixes

If either `MarkExplicitlyEscaping` or `TreatRValueAsLValue` fix
points to an argument-to-parameter conversion, let's add more
more clarifying argument to the locator to pinpoint the problem.

Author: xedin

lib/Sema/CSFix.cpp

@@ -119,6 +119,10 @@ bool TreatRValueAsLValue::diagnose(const Solution &solution,
 
 TreatRValueAsLValue *TreatRValueAsLValue::create(ConstraintSystem &cs,
                                    ConstraintLocator *locator) {
+  if (locator->isLastElement<LocatorPathElt::ApplyArgToParam>())
+    locator = cs.getConstraintLocator(
+        locator, LocatorPathElt::ArgumentAttribute::forInOut());
+
   return new (cs.getAllocator()) TreatRValueAsLValue(cs, locator);
 }
 
@@ -168,6 +172,10 @@ bool MarkExplicitlyEscaping::diagnose(const Solution &solution,
 MarkExplicitlyEscaping *
 MarkExplicitlyEscaping::create(ConstraintSystem &cs, Type lhs, Type rhs,
                                ConstraintLocator *locator) {
+  if (locator->isLastElement<LocatorPathElt::ApplyArgToParam>())
+    locator = cs.getConstraintLocator(
+        locator, LocatorPathElt::ArgumentAttribute::forEscaping());
+
   return new (cs.getAllocator()) MarkExplicitlyEscaping(cs, lhs, rhs, locator);
 }