Improve Navigation2D default settings, see #56852

This commit reduces `cell_size` and `edge_connection_margin` default
values so that `Navigation2D` behaves more like in Godot <= `3.4` by default.

doc/classes/ProjectSettings.xml

@@ -1329,10 +1329,10 @@
 			The policy to use for unhandled Mono (C#) exceptions. The default "Terminate Application" exits the project as soon as an unhandled exception is thrown. "Log Error" logs an error message to the console instead, and will not interrupt the project execution when an unhandled exception is thrown.
 			[b]Note:[/b] The unhandled exception policy is always set to "Log Error" in the editor, which also includes C# [code]tool[/code] scripts running within the editor as well as editor plugin code.
 		</member>
-		<member name="navigation/2d/default_cell_size" type="int" setter="" getter="" default="10">
+		<member name="navigation/2d/default_cell_size" type="int" setter="" getter="" default="1">
 			Default cell size for 2D navigation maps. See [method NavigationServer2D.map_set_cell_size].
 		</member>
-		<member name="navigation/2d/default_edge_connection_margin" type="int" setter="" getter="" default="5">
+		<member name="navigation/2d/default_edge_connection_margin" type="int" setter="" getter="" default="1">
 			Default edge connection margin for 2D navigation maps. See [method NavigationServer2D.map_set_edge_connection_margin].
 		</member>
 		<member name="navigation/3d/default_cell_size" type="float" setter="" getter="" default="0.3">

scene/resources/world_2d.cpp

@@ -83,8 +83,8 @@ World2D::World2D() {
 	// Create and configure the navigation_map to be more friendly with pixels than meters.
 	navigation_map = NavigationServer2D::get_singleton()->map_create();
 	NavigationServer2D::get_singleton()->map_set_active(navigation_map, true);
-	NavigationServer2D::get_singleton()->map_set_cell_size(navigation_map, GLOBAL_DEF("navigation/2d/default_cell_size", 10));
-	NavigationServer2D::get_singleton()->map_set_edge_connection_margin(navigation_map, GLOBAL_DEF("navigation/2d/default_edge_connection_margin", 5));
+	NavigationServer2D::get_singleton()->map_set_cell_size(navigation_map, GLOBAL_DEF("navigation/2d/default_cell_size", 1));
+	NavigationServer2D::get_singleton()->map_set_edge_connection_margin(navigation_map, GLOBAL_DEF("navigation/2d/default_edge_connection_margin", 1));
 }
 
 World2D::~World2D() {