D4135: Split implementation of keyboard layout handling into a dedicated class

bam added inline comments.

INLINE COMMENTS

> bam wrote in keyboard_input.cpp:709
> I'm not quite follow the check here and whole processModifiers() method:
> it's occurs after client gets the modifiers event, right?
> But at this moment, the modifiers are already updated on server, isn't it?
> Sorry I might miss something.

Or it's used for nested mode?

REPOSITORY
  R108 KWin

REVISION DETAIL
  https://phabricator.kde.org/D4135

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