Add Serialization test for nested protocols

Author: karwa

test/Serialization/Inputs/nested-protocols.swift

@@ -0,0 +1,11 @@
+public struct Outer {
+  public protocol Inner {
+    func foo()
+  }
+}
+
+extension Outer {
+  public protocol InnerInExtension {
+    func bar()
+  }
+}

test/Serialization/nested-protocols.swift

@@ -0,0 +1,13 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend -emit-module -module-name nestedprotocolsource -emit-module-path %t/nestedprotocolsource.swiftmodule -primary-file %S/Inputs/nested-protocols.swift -enable-experimental-feature NestedProtocols
+// RUN: %target-swift-frontend -emit-sil %s -I %t | Filecheck %s
+
+import nestedprotocolsource
+
+// CHECK: usesNested<A>(_:)
+// CHECK-NEXT: sil @$s4main10usesNestedyyx20nestedprotocolsource5OuterV5InnerRzlF :
+public func usesNested(_ x: some Outer.Inner) {}
+
+// CHECK: usesNestedInExtension<A>(_:)
+// CHECK-NEXT: sil @$s4main21usesNestedInExtensionyyx20nestedprotocolsource5OuterV05InnerdE0RzlF :
+public func usesNestedInExtension(_ x: some Outer.InnerInExtension) {}