For a single function, making an extension doesn't make much sense. Just use getActorTypeByName(_Name). For your "create actor at layer" suggestion, you don't even need code to do that. Simply make a custom block that creates an actor, and then uses the block that sends an actor to a specified layer.
<block tag="Get-Actor-Type-By-Name" spec="Actor Type of Name %0" code="getActorTypeByName(~)" type="normal" color="blue" returns="actortype"> <fields> <text order="0"></text> </fields></block>
my extension even not shown in the list of extensions.... I don't know what to write in hx file
Pathfinding would definitely be useful if it were boiled down into some format that beginners could understand.