Kernel: PID/TID typing

This compiles, and contains exactly the same bugs as before.
The regex 'FIXME: PID/' should reveal all markers that I left behind, including:
- Incomplete conversion
- Issues or things that look fishy
- Actual bugs that will go wrong during runtime

Kernel/Ptrace.cpp

@@ -43,7 +43,7 @@ KResultOr<u32> handle_syscall(const Kernel::Syscall::SC_ptrace_params& params, P
         return KSuccess;
     }
 
-    if (params.pid == caller.pid())
+    if (params.pid == caller.pid().value())
         return KResult(-EINVAL);
 
     Thread* peer = nullptr;