Adding regression test

Author: ahejlsberg

tests/cases/compiler/errorElaboration.ts

@@ -0,0 +1,12 @@
+// Repro for #5712
+
+interface Ref<T> {
+    prop: T;
+}
+interface Container<T> {
+    m1: Container<Ref<T>>;
+    m2: T;
+}
+declare function foo(x: () => Container<Ref<number>>): void;
+let a: () => Container<Ref<string>>;
+foo(a);