Using SDL's initialization logic, this is mainly a change for XDG
as LIBDECOR already required a configure event before accessing
the underlying XDG window.
While I didn't notice functional changes with this change window
flickering on startup remains an issue with some compositors
(KDE & river). Debugging these issues is simpler when both windowing
decoration systems work in a similar way & window configuration
is guaranteed to have run before the window is returned.
(via #xdg_surface_ack_configure).
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