fix: keyboard variants display incorrectly on upgrade

Earlier, keyboard variants were embedded in layouts in config. It is displayed incorrectly with new QML Keyboard Layout applet.

Now we need to update the config to split variants into separate configuration entry.

Code itself is still compatible with the old format, but should be refactored in the future.

Config update script sample:

- Input:
LayoutList=us,us(intl),ru,gb(dvorak),gb

- Output:
LayoutList=us,us,ru,gb,gb
VariantList=,intl,,dvorak
# DELETE LayoutList

CCBUG: 390079
@davidedmundson