First review round. Switched to batch option testing

- Re-enabled flang tests.
- Renamed class DriverController to DriverData, and made it a dataclass
- Removed the custom file validation code. argparse will handle most of this
- Redefined a few lists as sets and dictionaries
- Removed untested_sequence. It was unused in the end
- Removed find_supported_seq_cmp_start() in favour of bisect_left
- Removed the command preprocessing. The problem was not the automatic addition of "cc1" & "cc1as" options. "KIND_COMMAJOINED" was omitted from the prefix check. See the comment "this script cannot generate tests for" for details.
- Switched to creating Lit test run lines with batches of test options. Improves performance, and hopefully will make the tests run successfully on Windows.

Author: GeorgeKA