Sema: Add another test that passes with -enable-experimental-associated-type-inference

Author: slavapestov

test/decl/protocol/req/associated_type_inference_stdlib_2.swift

@@ -0,0 +1,23 @@
+// RUN: %target-typecheck-verify-swift -enable-experimental-associated-type-inference
+// RUN: not %target-typecheck-verify-swift
+
+protocol IP {
+  associatedtype E
+
+  func next() -> E?
+}
+
+protocol S {
+  associatedtype I: IP
+  associatedtype E where E == I.E
+
+  func makeI() -> I
+}
+
+struct G: S {
+  struct I: IP {
+    func next() -> Int? {}
+  }
+
+  func makeI() -> I {}
+}