D4220: Add a basic SNI for keyboard layout

bam added a comment.


  We are going to revert this in favor of https://invent.kde.org/plasma/plasma-desktop/-/merge_requests/181:
  it supports all the existing functional here plus missing one (problem with short layout names was solved):
  
  - flags and/or short text for the layouts
  
  If any objections, please tell.

REPOSITORY
  R108 KWin

REVISION DETAIL
  https://phabricator.kde.org/D4220

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