Follow up fixes to various PRs. (#13334)

- Ensure `MarlinUI:get_progress` is defined for `ExtUI`.
- Fix for `BACKLASH_SMOOTHING` with small segments.
  `BACKLASH_SMOOTHING` with extremely small segments failed to fully correct due to the correction factor being rounded down. Rounding up ensures the entire backlash will converge to zero even for small segments.
- Add pinout for the beta revision `EINSY_RETRO`.
- Update soft endstops with tool offsets (for toolchange et. al. move clamping) (#12568)