fdo#68546 Update settings for MenuBarWindow in InitStyleSettings

It updates menubar's text color settings in StyleSettings when user
changes persona.

Change-Id: Ic9c3e8073b9188a792823a84bf78b9b5976af50d
Reviewed-on: https://gerrit.libreoffice.org/8713
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>