More progress.

- AMBUSH flag on nodes makes them blind and untargetable when getting `startnode` and `goalnode` for `FindPath()`. This is useful for indicating a node should be skipped when tele/portaling, so the current path can be preserved.
- Setup is simple: place nodes behind lines that tele/portal entities and mark them as AMBUSH.

Other changes:

- Restored global array since blockmap is not a viable option here.
- Added MAPINFO `pathing` flag which enables pathing by default.
- Added NOPATHING flag to disable pathing entirely, useful for maps that have pathing enabled.
- Added `ReachedNode(Actor mo)` virtual, responsible for handling node traversal.
- Nodes now make use of MeleeRange to limit their sight checking functions.

src/p_setup.cpp

@@ -326,6 +326,7 @@ void FLevelLocals::ClearLevelData(bool fullgc)
 	}
 	ClearPortals();
 
+	PathNodes.Clear();
 	tagManager.Clear();
 	ClearTIDHashes();
 	if (SpotState) SpotState->Destroy();