Introduce qemu_win32_map_alloc() and qemu_win32_map_free() to allocate
shared memory mapping. The handle can be used to share the mapping with
another process.

Teach qemu_create_displaysurface() to allocate shared memory. Following
patches will introduce other places for shared memory allocation.

Other patches for -display dbus will share the memory when possible with
the client, to avoid expensive memory copy between the processes.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20230606115658.677673-10-marcandre.lureau@redhat.com>