Progress: Redesign the FSS identify functions.

Progress: Redesign the FSS identify functions.

Always reset the original used length on error.

Reduce the number of return statements.

Add a check for the combining joiner characters after the `#`.

Remove inaccurate comment about depending on `f_utf_is_combining()` from parse function.

Utilize the `f_state_t` locally to perform the necessary operations.
This is not exposed to the caller to prevent **API** and **ABI** breakage.
Future versions of **FLL** (0.9+) are expected to pass the state via the function parameter.

Switch to the new practice of using flags to manage special internal states.
This no longer guesses success based on `ids.used` being non-zero.
Using the internal flags allows accurate handling.

Add comments to functions that need `f_state_t` so that future version of **FLL** can properly handle.