Ensure that `as` and `from` are valid identifiers while their special
meaning in import statements is retained.

-- Testcase --
import { foo as bar } from 'mod';
import * as mod from 'mod';

function fn(as, from) {
	return as + from;
}

as = 1;
from = true;

printf("%.J\n", [
	bar,
	mod,
	fn(1, 2),
	as,
	from
]);
-- End --

-- File mod.uc --
export let foo = false;
export default 'test';
-- End --

-- Args --
-R -L files/
-- End --

-- Expect stdout --
[
	false,
	{
		"foo": false,
		"default": "test"
	},
	3,
	1,
	true
]
-- End --