gutils.c: Improve g_get_os_info() for Windows 10/Server 2019+

Hi,

This is the toned-down counterpart of MR !2351 (merged) where we improve retrieving version info for Windows 10/Server 2019 20H2 or later, as well as Windows 11.

Things are the same with what is done in MR !2351 (merged), except that we continue to indicate server versions as Windows 7/8/8.1/10 Server. Windows 11 is now correctly identified and Windows 10/Server 2019+ after 20H2 are also correctly identified as 21H1 and 21H2, etc.

This fixes issue #2443 (closed) on the glib-2-70 branch.

With blessings, thank you!