Fix pathfinder bugs: returning nil frequently, broken A*, jump through solid nodes (#9339)

* Fix pathfinder fail when startpos is over air
* Note down pathfinder restrictions
* Implement real A* search
* Pathfinder: Implement buildPath non-recursively
* Update find_path documentation
* Pathfinder: Check if jump path is unobstructed
* Pathfinder: Fix drop check first checking upwards
* Pathfinder: Return nil if source or dest are solid
* Pathfinder: Use priority queue for open list

builtin/game/features.lua

@@ -15,6 +15,7 @@ core.features = {
 	httpfetch_binary_data = true,
 	formspec_version_element = true,
 	area_store_persistent_ids = true,
+	pathfinder_works = true,
 }
 
 function core.has_feature(arg)