Kernel: Fix some problems with Thread::wait_on and Lock

This changes the Thread::wait_on function to not enable interrupts
upon leaving, which caused some problems with page fault handlers
and in other situations. It may now be called from critical
sections, with interrupts enabled or disabled, and returns to the
same state.

This also requires some fixes to Lock. To aid debugging, a new
define LOCK_DEBUG is added that enables checking for Lock leaks
upon finalization of a Thread.

Kernel/Scheduler.cpp

@@ -511,6 +511,21 @@ void Scheduler::invoke_async()
         pick_next();
 }
 
+void Scheduler::yield_from_critical()
+{
+    auto& proc = Processor::current();
+    ASSERT(proc.in_critical());
+    ASSERT(!proc.in_irq());
+
+    yield(); // Flag a context switch
+
+    u32 prev_flags;
+    u32 prev_crit = Processor::current().clear_critical(prev_flags, false);
+
+    // Note, we may now be on a different CPU!
+    Processor::current().restore_critical(prev_crit, prev_flags);
+}
+
 void Scheduler::notify_finalizer()
 {
     if (g_finalizer_has_work.exchange(true, AK::MemoryOrder::memory_order_acq_rel) == false)