`ToInteger` doesn't handle all expected cases.

For example, the ASL snippet `ToInteger("123abcd")` fails with `ParseFail(InvalidOperationOnObject { op: ToInteger, typ: String })`.

This is masked in the `aml_tester` test `to_integer.asl` because `iasl` optimizes out the call to ToInteger on a string constant. #277 has a little more detail on that (because it adds the `-oa` flag to `iasl` which unmasked this bug)
