[NTOSKRNL] Add a raw implementation of !irpfind in kdbg

[NTOSKRNL] Add a raw implementation of !irpfind in kdbg

This is far from perfect, and totally doesn't match the
WinDBG way of doing it. Instead of browsing pool to find
matching 'IRP' tags, we just browse all the processes
to find the queued IRP. This requires the IRPs to be queued,
obviously, and will make us miss the leaked IRPs, for instance.

Proper way to do it would be to implement !poolfind and then
rely on its implementation to find our IRPs.

Perhaps later ;-)