Add more syntax tests for enums and interfaces/libraries

test/libsolidity/syntaxTests/parsing/enum_from_interface.sol

@@ -0,0 +1,9 @@
+interface I {
+    enum Direction { Left, Right }
+}
+
+contract D {
+    function f() public pure returns (I.Direction) {
+      return I.Direction.Left;
+    }
+}