feat: newer rules around casting Data

* you cannot cast FROM Data with a `let`
* you cannot cast FROM Data by passing
  Data to none Data when calling a function
* you MUST use `assert` to cast from data
* you can cast INTO Data with a `let`
* you can cast INTO Data by passing none Data
  to Data when calling a function
* You cannot assert cast Data without an
  annotation

examples/acceptance_tests/050/lib/tests.ak

@@ -0,0 +1,40 @@
+use aiken/builtin
+
+pub type Thing {
+  wow: Int,
+}
+
+test assert_1() {
+  assert thing: Thing = builtin.constr_data(0, [builtin.i_data(1)])
+
+  thing.wow == 1
+}
+
+fn cast_to_thing(x: Data) -> Thing {
+  assert x: Thing = x
+
+  x
+}
+
+test assert_2() {
+  let thing = Thing { wow: 1 }
+
+  let still_thing = cast_to_thing(thing)
+
+  still_thing.wow == 1
+}
+// should not typecheck
+// test unlift_data_without_assert_1() {
+//   let thing: Thing = builtin.constr_data(0, [builtin.i_data(1)])
+//   thing.wow == 1
+// }
+
+// should not typecheck
+// fn bad_cast(x: Thing) -> Int {
+//   x.wow
+// }
+
+// test unlift_data_without_assert_2() {
+//   let thing = builtin.constr_data(0, [builtin.i_data(1)])
+//   bad_cast(thing) == 1
+// }