[CSSimplify] Allow l-value object simplication if l-value type is a placeholder

Placeholders propagate but we still can allow contextual inference,
to facilitate that the solver should consider `l-value object` constraint
to be solved and allow placeholders on "object" type.

Author: xedin

lib/Sema/CSBindings.cpp

@@ -1594,7 +1594,7 @@ PotentialBindings::inferFromRelational(Constraint *constraint) {
       if (type->isTypeVariableOrMember())
         return std::nullopt;
 
-     type = LValueType::get(type);
+      type = LValueType::get(type);
     } else {
       // Right-hand side of the l-value object constraint can only
       // be bound via constraint simplification when l-value type

lib/Sema/CSSimplify.cpp

@@ -14178,6 +14178,14 @@ ConstraintSystem::simplifyLValueObjectConstraint(
     return type->is<LValueType>();
   };
 
+  if (lvalueTy->isPlaceholder()) {
+    if (!shouldAttemptFixes())
+      return SolutionKind::Error;
+
+    recordAnyTypeVarAsPotentialHole(type2);
+    return SolutionKind::Solved;
+  }
+
   if (!isOrCanBeLValueType(lvalueTy)) {
     if (!shouldAttemptFixes())
       return SolutionKind::Error;