Implement 'body_is_shape_set_as_one_way_collision' in PhysicsServer2D

[Handagotes]

Hello!
One-way property of shapes in PhysicsServer2D is set-only for some reason. I suggest to implement a getter method 'body_is_shape_set_as_one_way_collision'.

Describe the project you are working on

2D platformer with heavy use of tile maps.

Describe the problem or limitation you are having in your project

I want to implement a feature that allows players to drop down through semisolid objects.
To do this, I need a reliable way to determine if the player is standing on semisolid object (with one-way collision).
I use Area2D and 'body_shape_entered' signal to do this.
For CollisionObject2D nodes this is trivial, because they have convenient 'is_shape_owner_one_way_collision_enabled' method.
Unfortunately, there is no easy way to do this for TileMapLayer, especially after GH-102662 being merged.

In 4.4 I used this code:

func _is_shape_one_way(body_rid: RID, body: Node2D, body_shape_index: int) -> bool:
	if body is PhysicsBody2D:
		return (body as CollisionObject2D).is_shape_owner_one_way_collision_enabled(body_shape_index)
	
	var tile_map_layer := body as TileMapLayer
	
	if tile_map_layer == null:
		return false
	
	var coords := tile_map_layer.get_coords_for_body_rid(body_rid)
	var tile_data := tile_map_layer.get_cell_tile_data(coords)
	
	for layer_id: int in range(tile_map_layer.tile_set.get_physics_layers_count()):
		if tile_data.get_collision_polygons_count(layer_id) <= body_shape_index:
			continue
		
		if not tile_data.is_collision_polygon_one_way(layer_id, body_shape_index):
			return false
	
	return true

In 4.5 I will not be able to use 'get_coords_for_body_rid' method because it will return physics quadrant coordinates instead of tile coordinates. Explanation

Describe the feature / enhancement and how it helps to overcome the problem or limitation

PhysicsServer2D has method 'body_set_shape_as_one_way_collision', but doesn't have a getter version of this method.
Method 'is_shape_set_as_one_way_collision' in PhysicsServer2D needs to be implemented. It will make one-way shape detection very easy.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

First of all, 'body_is_shape_set_as_one_way_collision' method must be added to PhysicsServer2D and in inherited classes.

bool GodotPhysicsServer2D::body_is_shape_set_as_one_way_collision(RID p_body, int p_shape_idx) const {
	GodotBody2D *body = body_owner.get_or_null(p_body);
	ERR_FAIL_NULL_V(body, false);
	ERR_FAIL_INDEX_V(p_shape_idx, body->get_shape_count(), false);

	return body->is_shape_set_as_one_way_collision(p_shape_idx);
}

This method must be exposed to engine users as well.
After this, one-way shape detection with Area2D becomes very trivial:

func _is_shape_one_way(body_rid: RID, body_shape_index: int) -> bool:
	return PhysicsServer2D.body_is_shape_set_as_one_way_collision(body_rid, body_shape_index)

If this enhancement will not be used often, can it be worked around with a few lines of script?

Workaround would require using RayCast2D with or instead of Area2D.
This will allow me to write something like this:

...
var coords := tile_map_layer.local_to_map(ray_cast.get_collision_point())
var tile_data := tile_map_layer.get_cell_tile_data(coords)
...

I see this workaround as a crutch - the player can stand on different shapes simultaneously, which can result in false semisolid detection. To counter this, I would need more than one RayCast2D.
This idea gets ugly pretty fast when I try to consider all in-game situations.

Is there a reason why this should be core and not an add-on in the asset library?

Addons cannot expose internal engine API as far as I know.
Maybe it can be implemented using GDNative plugin, but I'm not sure.
In any case, using separate plugin to expose single getter for property is ugly.
I just can't think of any good reason why one-way property for shapes must be set-only in PhysicsServer2D.

[Handagotes]

Today I tried to implement this feature in forked godot repo and it worked great!
I also noticed that there are some other set-only properties in PhysicsServer2D. Is there a good reason for that? If no, I can create pull-request and add getters for some of them too.