This fixes an out-of-bounds index access when the node resolver was already applied to the schematic (i.e. biome decoration).
Also improves the handling of the two cases: prior node resolving (m_nodenames), and after node resolving (manual lookup)
* Rename IWritableNodeDefManager to NodeDefManager
* Make INodeDefManager functions const
* Use "const *NodeDefManager" instead of "*INodeDefManager"
* Remove unused INodeDefManager class
* Merge NodeDefManager and CNodeDefManager
* Document NodeDefManager