locale1: fix use-after-free in xkb_keymap creation

qPrintable creates temporary objects that are destroyed before
`xkb_keymap_new_from_names` is called. It's highly likely that the data
we pass to xkbcommon will be overwritten by random data by that point.

Fix that by storing values as QByteArrays just like
`Xkb::loadKeymapFromConfig` does.


(cherry picked from commit f70bda9f)