AK: Make quick_sort() a little more ergonomic

Now it actually defaults to "a < b" comparison, instead of forcing you
to provide a trivial less-than comparator. Also you can pass in any
collection type that has .begin() and .end() and we'll sort it for you.

Kernel/Scheduler.cpp

@@ -401,7 +401,7 @@ bool Scheduler::pick_next()
         sorted_runnables.append(&thread);
         return IterationDecision::Continue;
     });
-    quick_sort(sorted_runnables.begin(), sorted_runnables.end(), [](auto& a, auto& b) { return a->effective_priority() >= b->effective_priority(); });
+    quick_sort(sorted_runnables, [](auto& a, auto& b) { return a->effective_priority() >= b->effective_priority(); });
 
     Thread* thread_to_schedule = nullptr;