[Test] Add some TBDGen test cases for enum case witnesses

Author: theblixguy

test/TBD/enum_case_protocol_witness.swift

@@ -0,0 +1,23 @@
+// REQUIRES: VENDOR=apple
+// RUN: %target-swift-frontend -emit-ir -enable-testing -o/dev/null -module-name test -validate-tbd-against-ir=all %s
+// RUN: %target-swift-frontend -emit-ir -o/dev/null -module-name test -validate-tbd-against-ir=all %s
+
+protocol ProtoInternal {
+  static var bar1: Self { get }
+  static func bar2(arg: Int) -> Self
+}
+
+enum EnumInternal: ProtoInternal {
+  case bar1
+  case bar2(arg: Int)
+}
+
+public protocol ProtoPublic {
+  static var bar3: Self { get }
+  static func bar4(arg: Int) -> Self
+}
+
+public enum EnumPublic: ProtoPublic {
+  case bar3
+  case bar4(arg: Int)
+}