Move NT process-telemetry declarations into a public header

[mikeagun]

Summary

PsGetProcessStartKey is implemented on top of the native NT
PROCESS_TELEMETRY_ID_INFORMATION structure and the NtQueryInformationProcess
API. Per Microsoft's documentation these have no public SDK header and must be
declared by hand, and today usersim declares them privately inside src/ps.cpp.
Because the declarations live in a .cpp, anything else that needs the same
native definitions cannot reuse them and has to maintain a separate,
drift-prone copy.

Promote those declarations to a public leaf header,
inc/usersim/nt_process_info.h, so they are defined once and can be reused by
usersim consumers.

Changes

• Add inc/usersim/nt_process_info.h declaring PROCESS_TELEMETRY_ID_INFORMATION,
  the ProcessTelemetryIdInformation information-class value, and the
  NtQueryInformationProcess_t function-pointer typedef.
• src/ps.cpp includes the new header and drops its local declarations; the
  PsGetProcessStartKey logic is unchanged.
• Register the header in src/usersim.vcxproj.

Design notes

The header is intentionally a leaf: it declares only native NT types and depends
solely on basic Windows types (ULONG/HANDLE/NTSTATUS/NTAPI/...), with no
usersim platform dependencies, so it can be included on its own without pulling
in usersim's internal headers. NtQueryInformationProcess_t uses ULONG for the
information-class parameter so the header does not also need to carry a
PROCESSINFOCLASS enum.

Testing

• usersim builds clean (Debug/x64); no functional change.
• The new header is self-contained and compiles when included standalone.

Context

Prompted by review of the corresponding eBPF for Windows change
(microsoft/ebpf-for-windows#5383).