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

bam added inline comments.

INLINE COMMENTS

> keyboard_input.cpp:709
>      m_modifiersChangedSpy->updateModifiers(modifiers());
> +    m_keyboardLayout->checkLayoutChange();
>  }

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.

REPOSITORY
  R108 KWin

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

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