META: pathfinder performance improvement ideas

[lynxlynxlynx]

Just ideas, some already partially tested. Edit as more are thought of:

• Refactor Point to hide navmap<->tilemap coordinate conversions #1693
  • IsWalkableTo should work faster when done strictly in the search map space
  • cache actor Pos in search map space to avoid repeated conversions?
• consider splicing sub paths for bumping (instead find the bumped position, then calculate a path from that position to the current position in the path and then prepend that path segment, which would be much better than completely recalculating a path)
• we probably don't make any effort to avoid calculating a path that will bump again
• should an actor be able to bump more than one other actor?
• consider using squared distances in FindPath (at minimum the heuristic factor would need adjusting) to skip a bunch of sqrts
• try an approximation for std::hypot in NormalizeDeltas
• Search map with a walk flag #1840
• Unreachable searchmap islands cause performance degradation Unreachable searchmap islands cause performance degradation #2079
• approach doors with only one actor
• Going to open a door with the full party make it drop fps considerably  #1692
  • reuse a little bit of information to halve the penalty by skipping the ignore-actors run if there wasn't any actor to potentially bump into Going to open a door with the full party make it drop fps considerably  #1692 (comment)
• parallelize FindPath
• if Movable::DoStep is also hot, we could optimise the lookahead loop to not iterate over potentially all actors on the map 6+ times and using a GetAllActorsInRect to get a subset first and then manually do the checks that GetActor does