Revert "Revert "Handle XdgShell window geometry in configure request sizes""
Plasma 5.16 has branched, and support is now in Frameworks with
https://cgit.kde.org/kwayland.git/commit/?id=6da6c7c7e090c024a8288088f9b96ef2bacf38a5,
So this can go into KWin master now.
This reverts commit 24cbe48656b7d4d6dffff86da8f81a522fff99e1.