Profiler: Add TimelineView widget and make the timeline cursor global

There's no longer a cursor in each process timeline, instead the parent
widget keeps track of it (along with the selection) and it all moves
in sync.

Userland/DevTools/Profiler/TimelineView.cpp

@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "TimelineView.h"
+#include <LibGUI/BoxLayout.h>
+
+namespace Profiler {
+
+TimelineView::TimelineView()
+{
+    set_layout<GUI::VerticalBoxLayout>();
+    set_shrink_to_fit(true);
+}
+
+TimelineView::~TimelineView()
+{
+}
+
+}