Now that AF_UNIX has come to Windows, update the existing logic in
qemu_chr_compute_filename() and qmp_chardev_open_socket() for Windows.

Signed-off-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20220802075200.907360-4-bmeng.cn@gmail.com>