add test file for deprecated conformances

Author: tayloraswift

TestModules/Snippets/DeprecatedConformances.swift

@@ -0,0 +1,22 @@
+public
+protocol P {}
+
+extension P
+{
+    public
+    func f() {}
+}
+
+public
+struct S {}
+
+@available(*, deprecated)
+extension S:P
+{
+}
+@available(*, deprecated)
+extension S
+{
+    public
+    func g() {}
+}