dropUntil

assert([1, 2, 3].dropWhile(1) == [2, 3]);
assert([1, 1, 1, 2, 3].dropWhile(1) == [2, 3]);
assert([1, 2, 3].dropWhile(2) == [1, 2, 3]);
assert(`aabc`.dropWhile('a') == `bc`); // TODO: Remove restriction on cast to dchar