GN-5233: mandataris-rank - take diaeresis into account

[elpoelma]

Overview

This PR ensures that letters with a diaeresis are taken into account when converting mandatee ranks to numbers.

connected issues and PRs:

GN-5233

How to test/reproduce

• Open the frontend
• Create/open an IV
• Ensure the 'IVGR4-LMB-1-rangorde-gemeenteraadsleden' is configured somewhere; and the source data (gemeenteraad) should contain at least 24 mandatees
• Sync the meeting
• Ensure the mandatees are correctly ordered based on rank (including 'TWEEËNTWINTIGSTE' and 'DRIEËNTWINTIGSTE')

Checks PR readiness

• UI: works on smaller screen sizes
• UI: feedback for any loading/error states
• Check cancel/go-back flows
• Check database state correct when deleting/updating (especially regarding relationships)
• changelog
• npm lint
• no new deprecations