Fix build breaks when linking with usersim againt code built against cxplat_kernel

[Alan-Jowett]

This pull request includes changes to the USERSIM_API to add new functions and improve error handling in ke.cpp. The most important changes include adding new API functions for querying processor counts and refining error handling in the KeSetSystemGroupAffinityThread function.

Additions to USERSIM_API:

• Added KeQueryActiveProcessorCount and KeQueryActiveProcessorCountEx functions to inc/usersim/ke.h to provide API access for querying active processor counts.

Implementation of new functions:

• Implemented KeQueryActiveProcessorCount and KeQueryActiveProcessorCountEx functions in src/ke.cpp to call the corresponding maximum processor count functions.

Error handling improvements:

• Improved error handling in the KeSetSystemGroupAffinityThread function by conditionally using UNREFERENCED_PARAMETER for the error variable in non-debug builds, and asserting error in debug builds.