Add navigation mesh source geometry parsers and callbacks

[smix8]

Add navigation mesh source geometry parsers and callbacks so that externals can hook their own geometry into the internal navigation mesh baking process.

Proposal godotengine/godot-proposals#5138

This can be used to hook addons, modules and extensions into the navigation mesh baking process.

E.g. Terrain3D or VoxelTool to name some examples. What all those extensions have currently in common is that they need to use suboptimal processes to add their geometry for navmesh baking and can't work frictionless with the default baking.

If a parser with callback is registered the Callable will be called for every single node that gets parsed when the NavigationServer parse_source_geometry_data() is used by something.

The Callable will get called with 3 args, the navigation mesh for the parse and bake properties, the source geometry object to add geometry to, and the actual node that gets parsed.

If the parser is no longer needed, e.g. because addon gets disabled, free the parser RID with the NavigationServer.

2D

var source_geometry_parser: RID
var source_geometry_parser_callback: Callable

func _ready() -> void:
	source_geometry_parser_callback = Callable(self, "_on_source_geometry_parser_callback")
	source_geometry_parser = NavigationServer2D.source_geometry_parser_create()
	NavigationServer2D.source_geometry_parser_set_callback(source_geometry_parser, source_geometry_parser_callback)

func _on_source_geometry_parser_callback(
	p_navigation_mesh: NavigationPolygon,
	p_source_geometry_data: NavigationMeshSourceGeometryData2D,
	p_parsed_node: Node) -> void:
	pass
	# Add custom source geometry to p_source_geometry_data.
	# The p_navigation_mesh holds the parse settings. Do NOT edit or add directly to p_navigation_mesh.
	# The p_parsed_node is the currently parsed node.

func delete_parser() -> void:
	NavigationServer2D.free_rid(source_geometry_parser)
	source_geometry_parser = RID()

3D

var source_geometry_parser: RID
var source_geometry_parser_callback: Callable

func _ready() -> void:
	source_geometry_parser_callback = Callable(self, "_on_source_geometry_parser_callback")
	source_geometry_parser = NavigationServer3D.source_geometry_parser_create()
	NavigationServer3D.source_geometry_parser_set_callback(source_geometry_parser, source_geometry_parser_callback)

func _on_source_geometry_parser_callback(
	p_navigation_mesh: NavigationMesh,
	p_source_geometry_data: NavigationMeshSourceGeometryData3D,
	p_parsed_node: Node) -> void:
	pass
	# Add custom source geometry to p_source_geometry_data.
	# The p_navigation_mesh holds the parse settings. Do NOT edit or add directly to p_navigation_mesh.
	# The p_parsed_node is the currently parsed node.

func delete_parser() -> void:
	NavigationServer3D.free_rid(source_geometry_parser)
	source_geometry_parser = RID()

[smix8]

@Zylann and @TokisanGames might be interested in (reviewing) this.

[fire]

I did not do a technical review.

Would be good to squeeze into 4.3 as it would be many more months of hanging dry addons and extensions that can not really get their users to use the hot master build.

Would be good for gdextension authors as a quality of life enhancement.

[TokisanGames]

@tcoxon is our resident expert on navigation in Terrain3D.

[akien-mga]

Thanks!