Update liblouis to 3.21.0

[aaclause]

Link to issue number:

Fixes #13408

Summary of the issue:

Liblouis 3.21.0 has been released.

Description of how this pull request fixes the issue:

Updates liblouis to 3.21.0 which mainly brings major updates for Hungarian and German. Changelog.

Testing strategy:

Ran from sources and loaded the new braille tables. LGTM.

Known issues with pull request:

None

Change log entries:

Section: Changes

- Updated liblouis braille translator to [3.21.0 https://github.com/liblouis/liblouis/releases/tag/v3.21.0]. (#13438)
  - Added new German 6 dot computer braille table.
- Added Catalan grade 1 braille table. (#13408)

Code Review Checklist:

• Pull Request description:
  • description is up to date
  • change log entries
• Testing:
  • Unit tests
  • System (end to end) tests
  • Manual testing
• API is compatible with existing add-ons.
• Documentation:
  • User Documentation
  • Developer / Technical Documentation
  • Context sensitive help for GUI changes
• UX of all users considered:
  • Speech
  • Braille
  • Low Vision
  • Different web browsers
  • Localization in other languages / culture than English