test(lean): add simple example of notation implemented using Lua

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>

tests/lean/run/n1.lean

@@ -0,0 +1,15 @@
+variable A : Type.{1}
+variable a : A
+variable g : A → A
+variable f : A → A → A
+
+(*
+function foo()
+  return Const("g")(parse_expr())
+end
+*)
+
+notation `tst` c1:(call foo) `with` c2:(call foo) := f c1 c2
+notation `simple` c:(call foo) := c
+variable b : A
+check tst (simple b) with a