Implement way to handle multiple `NavigationAgent2d` character sizes

[Abb4]

Followup to https://github.com/Abb4/earie-treasures/pull/30, specifically https://github.com/Abb4/earie-treasures/pull/30#issuecomment-1676478024

Broader Discussion and problem statement: https://github.com/Abb4/earie-treasures/discussions/71

Important: If we work with NavigationMaps it is important to let the navigation server load the maps by skipping a frame:

public override void _Ready()
{
    // ...

    // Make sure to not await during _Ready.
    // see more: https://docs.godotengine.org/en/stable/tutorials/navigation/navigation_introduction_2d.html#setup-for-2d-scene
    Callable.From(ActorSetup).CallDeferred();
}

private async void ActorSetup()
{
    // Wait for the first physics frame so the NavigationServer can sync and create navigation map
    await ToSignal(GetTree(), SceneTree.SignalName.PhysicsFrame);

    navigationReady = true;
}

Here is what I could find:

• a user smix attempted to create baking step for the TileMap but gave up: https://github.com/godotengine/godot/pull/70724#issuecomment-1572468095 https://github.com/godotengine/godot/pull/80796
  • here their reply on our exact issue: https://www.reddit.com/r/godot/comments/13sjdov/godot_402_navigationagent2d_getting_stuck_on_walls/?rdt=52072
• comment describing how to create nav meshes for different sizes for 3d (need to port to 2d and adjust for TileMap, scroll down for code): https://github.com/godotengine/godot-proposals/issues/5542#issue-1396270101
• somebody implemented code to create polygons from tile maps, but its 1 year old and written in gdscript: https://github.com/Black-Virtue/Godot4-Navigation-with-TileMaps/blob/main/TileMapHelper.gd
• docs on NavigationObstacles: https://docs.godotengine.org/en/stable/tutorials/navigation/navigation_using_navigationobstacles.html#doc-navigation-using-navigationobstacles
• docs on NavigationAgents: https://docs.godotengine.org/en/stable/tutorials/navigation/navigation_using_navigationagents.html#navigationagent-script-templates
• docs on NavigationMeshes: https://docs.godotengine.org/en/stable/tutorials/navigation/navigation_using_navigationmeshes.html
• docs on TileMaps: https://docs.godotengine.org/en/latest/tutorials/2d/using_tilemaps.html
• docs on NavigationServer: https://docs.godotengine.org/en/latest/tutorials/navigation/navigation_using_navigationservers.html
  • discussion on multiple layers in tilemaps: https://github.com/godotengine/godot/issues/69743#issuecomment-1600236854
• a user claims to have solved the issue with code here: https://github.com/godotengine/godot/issues/60546#issuecomment-1656908403

[Abb4]

see navmesh complexity discussion: https://github.com/Abb4/earie-treasures/discussions/71