kernel: Add a way to lookup specific threads

kernel/src/thread/Scheduler.cpp

@@ -409,6 +409,16 @@ namespace Scheduler
         return {};
     }
 
+    Option<Thread*> find_by_tid(pid_t tid)
+    {
+        for (auto* const thread : g_threads)
+        {
+            if (thread->tid == tid) return thread;
+        }
+
+        return {};
+    }
+
     bool has_children(Process* process)
     {
         bool result { false };

kernel/src/thread/Scheduler.h

@@ -38,6 +38,7 @@ namespace Scheduler
     LinkedList<Process> check_for_dead_processes();
 
     Option<Process*> find_by_pid(pid_t pid);
+    Option<Thread*> find_by_tid(pid_t tid);
 
     template <typename Callback> void for_each_child(Process* process, Callback callback)
     {