virtio-gpu/win32: allocate shareable 2d resources/images

Allocate pixman bits for scanouts with qemu_win32_map_alloc() so we can
set a shareable handle on the associated display surface.

Note: when bits are provided to pixman_image_create_bits(), you must also give
the rowstride (the argument is ignored when bits is NULL)

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20230606115658.677673-11-marcandre.lureau@redhat.com>