cairo_surface_destroy() is called after the buffer is released, for every
wl_buffer. Windows usually reference their cairo surface before rendering,
so that extra reference is consumed after the buffer is released, so do
the same with cursor surfaces and add an extra reference whenever a cursor
surface change is about to be scheduled.
Otherwise, the GdkWaylandCursor is left with an invalid cairo_surface_t,
which causes crashes the next time it is used.
https://bugzilla.gnome.org/show_bug.cgi?id=735830
We want a surface so we can properly represent the scale factor for it.
All backends are converted to use surfaces and we reimplement the
backwards compat code in the generic code.
The cursor buffer is only non-null when a cursor is created from pixbuf,
so it is not necessary to keep track of whether to free this buffer on
finalize.
By keeping a pointer to the wl_cursor struct in GdkWaylandCursor, it is
no longer necessary to duplicate cursor data (width, height, hotspots,
etc.) between wl_cursor and GdkWaylandCursor.
The check for GDK_CURSOR_IS_PIXMAP was ineffective, since _all_
cursors have this type, from the looks of it. Instead, store
buffer ownership information separately.
This means we don't have to have hardcoded "/usr/share/wayland" to find the
cursors.
This change also fixes up the warning messages for when loading fails.
