in rtl we change the x pos. To change the x pos we need a y pos to go
with it, and taking the y pos before we get the true (0) top decoration
size of menu and menu-like widgets means rtl popdowns like the color
and highlight popdowns are vertically misplaced

there's no reason that a window would share the same decoration value
as its parent

Change-Id: I8cd1e96bb8ef7b0b728ff1baac5ee069325f9753
Reviewed-on: https://gerrit.libreoffice.org/43458Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>