Improve hardened UNC path checks for case insensitivity & missing split

[Steffen Winternheimer]

Currently we are using "-notcontains" as a logical check, which unfortunately checks for case sensitivity.
Update the logic to make it case insensitive.

https://stackoverflow.com/questions/74216620/powershell-contains-check-without-casesensitive

Also, 18.6.14.1 B split is missing from Windows 10 and 11 Stand-alone benchmarks.