[asl] Differentiate accessers with/without any args

[HadrienRenaud]

This PR implements checks that differentiate accessers with from without []. For example:

getter f1[] => integer
begin return 0; end

getter f2 => integer
begin return 0; end

func main () => integer
begin
  let x = f1[];
  let x = f2;

  return 0;
end

Before this PR, the two syntaxes could be used without distinction.

Also fixes a bug on make test-aarch64-asl.

[maranget]

Thanks @HadrienRenaud. Merge on its way.