padOsd: Figure out label/edition UI positions from unchanged fonts

padOsd: Figure out label/edition UI positions from unchanged fonts

We can figure out the position to render the text without resorting to
font sizes that make the whole text element sub-pixel size. As the
original labels in the SVG are themed invisible anyway, calculate the
button/ring/strip label and configuration UI position from their unchanged
size/location.

Closes: https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/5415
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2288>