Update bundled libxkbcommon version to 0.4.0

This release comes with important bug fixes. Also we can now
remove the workaround code which was needed for libxkbcommon 0.2.0.

Task-number: QTBUG-31712
Task-number: QTBUG-33732
Task-number: QTBUG-34056

Change-Id: I57caf7f803b9a01a15541a5ad82e464de3b8abbb
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Fix typos in QRegExp documentation

Change-Id: I80bce716ac1c161fd87291ecdbf21eb8f3f25e5a
Reviewed-by: André Hartmann <aha_1980@gmx.de>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>