[CSClosure] Teach syntactic element constraint generator about result builders

Closures and functions that have result builder transform applied have to be
handled specially by the constraint generator because transformed body is
associated with the context (function or closure) only during solution application.

include/swift/Sema/ConstraintSystem.h

@@ -3734,6 +3734,14 @@ public:
     return known->second;
   }
 
+  Optional<AppliedBuilderTransform>
+  getAppliedResultBuilderTransform(AnyFunctionRef fn) const {
+    auto transformed = resultBuilderTransformed.find(fn);
+    if (transformed != resultBuilderTransformed.end())
+      return transformed->second;
+    return None;
+  }
+
   void setCaseLabelItemInfo(const CaseLabelItem *item, CaseLabelItemInfo info) {
     assert(item != nullptr);
     assert(caseLabelItems.count(item) == 0);