gdkwindow-x11: Fix graphical regression from 5e325c4

Before 5e325c4, the default BitGravity was NorthWestGravity.
When static gravities were removed in 5e325c4, the BitGravity regressed
to the X11 default, Forget. Forget causes giant graphical glitches and
black flashes when resizing, especially in some environments that aren't
synchronized to a paint clock yet, like XWayland.

I'm assuming that the author assumed that the default of BitGravity was
NorthWestGravity, which is the default of WinGravity. Just go ahead and
fix this regression to make resizing look smooth again.
Get duplex option via IPP

Request "sides-supported" and "sides-default" attributes through
IPP if there is no PPD for selected printer.
Pass "sides" option with other options in printer_get_options().
Add function setup_ipp_option() for creating of IPP option
of given name with passed choices and default value.
Mark such an option as "is-ipp-option" so we can distinguish it
later.

https://bugzilla.gnome.org/show_bug.cgi?id=725441