CORE-19946
Adapted from PR #7577
This function tests whether a window has a window procedure that resides in kernel mode.
It is not documented by Microsoft, but unofficial (3rd party) documentation[^1] exists.
It is required and used internally by uxtheme.dll from Windows XP/2003/Vista/7/etc.
[^1]: https://undoc.airesoft.co.uk/user32.dll/IsServerSideWindow.php
Co-authored-by: Mohammad Amin Mollazadeh <[email protected]>