[NTOS:EX] Clarify the situation with the SystemPathInformation class. (#4065)

[NTOS:EX] Clarify the situation with the SystemPathInformation class. (#4065)

Since NT 3.51, this information class is trivially implemented.
The path to the NT directory is now stored in KUSER_SHARED_DATA
as the NtSystemRoot member.
Windows Checked builds show the following message and break to
the debugger before failing the function as not implemented:

EX: SystemPathInformation now available via SharedUserData

See https://www.geoffchappell.com/studies/windows/km/ntoskrnl/api/ex/sysinfo/query.htm
and https://www.geoffchappell.com/studies/windows/km/ntoskrnl/inc/api/ntexapi_x/kuser_shared_data/index.htm
for more information.