Kernel: Make Thread use AK::Time internally

This commit is very invasive, because Thread likes to take a pointer and write
to it. This means that translating between timespec/timeval/Time would have been
more difficult than just changing everything that hands a raw pointer to Thread,
in bulk.

Kernel/Tasks/SyncTask.cpp

@@ -38,7 +38,7 @@ void SyncTask::spawn()
         dbgln("SyncTask is running");
         for (;;) {
             VFS::the().sync();
-            (void)Thread::current()->sleep({ 1, 0 });
+            (void)Thread::current()->sleep(Time::from_seconds(1));
         }
     });
 }