[PATCH] xkb: fix build with libxkbcommon 1.6.0 and later

[PATCH] xkb: fix build with libxkbcommon 1.6.0 and later

A few XKB_KEY_dead_* defines got removed from 1.6.0. See also
https://github.com/xkbcommon/libxkbcommon/blob/6073565903488cb5b9a8d37fdc4a7c2f9d7ad04d/NEWS#L9-L14
https://gitlab.freedesktop.org/xorg/proto/xorgproto/-/merge_requests/70/diffs?commit_id=cb44799b72f611eb4c9d7cc185bc3b09e070be08

Pick-to: 6.6 6.5 6.2 5.15
Fixes: QTBUG-117950
Change-Id: I55861868f2bb29c553d68365fa9b9b6ed01c9aea
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
Gbp-Pq: Name libxkbcommon_1.6.0.diff