Kernel: When a lock is busy, donate remaining process ticks to lock holder.

Since we know who's holding the lock, and we're gonna have to yield anyway,
we can just ask the scheduler to donate any remaining ticks to that process.

WindowServer/WSWindowManager.cpp

@@ -130,6 +130,7 @@ void WSWindowManager::flip_buffers()
 WSWindowManager::WSWindowManager()
     : m_screen(WSScreen::the())
     , m_screen_rect(m_screen.rect())
+    , m_lock("WSWindowManager")
 {
 #ifndef DEBUG_COUNTERS
     (void)m_compose_count;