Traditionally, getter/setter functions have been considered a
C convenience, and we therefore didn't bother to add them for
many properties that are only consumed from JS.
However now that gjs optimizes property accesses by calling the
appropriate getter/setter instead, it makes sense to add them.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3620>
Move the get_preferred_width/height() and allocate() vfunc
implementations of WindowPreview to C, subclassing the C GObject from
JS.
This gets us another significant performance gain, allocating a
workspace with 20 windows now only takes 1.2 ms.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1743>