[ENGINE] Convert existing walkTo using tasks to use new task system

[Jameskmonger]

walkTo is broken (not in sync with server ticks) so need to convert all plugins using it to the new task system.

PR #406 has started this, see c5dc578 for an example way to introduce easily.

• create ActorActorInteractionTask (make actor walk towards some other actor) 91414d6 refactor: migrate npc interaction walkTo hooks to task system #411

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• item on npc 00bb8af refactor: migrate npc interaction walkTo hooks to task system #411
• item on object
• item on player 2a77f14 refactor: convert player_interaction and item_on_player to task system #412
• item on world item (not needed, no legacy walkTo)
• npc interaction cc357e4 refactor: migrate npc interaction walkTo hooks to task system #411
• object interaction c5dc578 refactor: migrate object_interaction walkTo hooks to use task system automatically #406
• player interaction 2a77f14 refactor: convert player_interaction and item_on_player to task system #412
• world item interaction 2a54908 refactor: migrate object_interaction walkTo hooks to use task system automatically #406