New hierarchy traversing functions

[NewboO]

Follow-up of #4603

Currently we have GraphNode.find, GraphNode.findOne and GraphNode.forEach to traverse a specific node (included) and all its descendants. The first two are also used in Entity.findComponent and Entity.findComponents (and possibly Entity.findScript and Entity.findScripts if #5851 is accepted and merged).

The main idea is to add the same functions for ancestors but in the original PR, we were debating about whether these functions should include the current node or not. This led to also add function for descendants only (thus excluding current node), the same way GraphNode.findByTag and GraphNode.findByPath currently work.