Improve Editor performance with large scene hierarchies

Use https://github.com/Tryibion/FlaxPerformanceTest as a reference test point and spawn 10k cubes in the root of the scene. Editor UI update and draw performance should be perfectly stable thus we need to:
* profile current state (with Tracy and with C# profiling like dotTrace or Visual Studio)
* update only visible controls (currently `TreeNode` tick when expanded and enabled)
* draw only visible controls (`ContainerControl` already has some culling mechanism but for tree hierarchy, we can do better)
* use some smart-logic for mouse events (`OnMouseXXX`) to skip iterating over all controls in tree node