Fix popup damage issues when toplevel and/or popup uses geometry

[RyanDwyer]

The wlr_xdg_popup_get_toplevel_coords function has the following quirks:

• It does not do anything with the coordinates of the passed popup. Instead, we are required to add them ourselves, which we do by passing them to the function as the surface local values.
• It adds the geometry (shadows etc) of the toplevel itself, so the coordinates are surface local rather than content local. For this reason, we have to negate the toplevel's geometry (child->view->geometry).
• I may be wrong, but the popup positions appear to be stored in surface local coordinates rather than content local coordinates. The geometry (shadows etc) of the popup itself must be negated (surface->geometry).

Fixes #2893.

[ddevault]

Thanks!

[emersion]

We can probably improve wlr_xdg_popup_get_toplevel_coords