fix: [1/2] Keyboard Layout applet: layout Name doesn't fit if variant is set

Layout variants were embedded in layout names as in us(intl).
Such name is too wide to fit in the applet.
Better just keep variants separate in their own config entry.
It's also a more structured and natural way to handle it.

@davidedmundson

KWin part:
kwin!479 (merged)

Corresponding update script converting old config format:
!269 (merged)