keyboard: Stop offsetting the focus rectangle

keyboard: Stop offsetting the focus rectangle

The focus rectangle of the OSK currently gets stored with an offset that
removes the global coordinates and makes it window-local coordinates.
This offsetting has been applied since the introduction of the
FocusTracker with commit fc5ab4470445992b1ad4338290deb24e6b1c5ce2 and it
seems there's no real reason for it.

By removing this, we also emit position-changed when the window has
moved but the window-local coordinates stayed the same. We really want
to emit position-changed in that case because it might affect whether
the window needs to be shifted up.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1728>