Mention that Area2D doesn't support one_way_collision

(cherry picked from commit c836bdf5b117c0262ca0794443da80fc3aba7ed3)

doc/classes/CollisionPolygon2D.xml

@@ -19,6 +19,7 @@
 		</member>
 		<member name="one_way_collision" type="bool" setter="set_one_way_collision" getter="is_one_way_collision_enabled" default="false">
 			If [code]true[/code], only edges that face up, relative to [CollisionPolygon2D]'s rotation, will collide with other objects.
+			[b]Note:[/b] This property has no effect if this [CollisionPolygon2D] is a child of an [Area2D] node.
 		</member>
 		<member name="one_way_collision_margin" type="float" setter="set_one_way_collision_margin" getter="get_one_way_collision_margin" default="1.0">
 			The margin used for one-way collision (in pixels). Higher values will make the shape thicker, and work better for colliders that enter the polygon at a high velocity.

doc/classes/CollisionShape2D.xml

@@ -20,6 +20,7 @@
 		</member>
 		<member name="one_way_collision" type="bool" setter="set_one_way_collision" getter="is_one_way_collision_enabled" default="false">
 			Sets whether this collision shape should only detect collision on one side (top or bottom).
+			[b]Note:[/b] This property has no effect if this [CollisionShape2D] is a child of an [Area2D] node.
 		</member>
 		<member name="one_way_collision_margin" type="float" setter="set_one_way_collision_margin" getter="get_one_way_collision_margin" default="1.0">
 			The margin used for one-way collision (in pixels). Higher values will make the shape thicker, and work better for colliders that enter the shape at a high velocity.

scene/2d/collision_polygon_2d.cpp

@@ -32,6 +32,7 @@
 
 #include "collision_object_2d.h"
 #include "core/engine.h"
+#include "scene/2d/area_2d.h"
 #include "scene/resources/concave_polygon_shape_2d.h"
 #include "scene/resources/convex_polygon_shape_2d.h"
 
@@ -273,6 +274,9 @@ String CollisionPolygon2D::get_configuration_warning() const {
 			warning += TTR("Invalid polygon. At least 2 points are needed in 'Segments' build mode.");
 		}
 	}
+	if (one_way_collision && Object::cast_to<Area2D>(get_parent())) {
+		warning += TTR("The One Way Collision property will be ignored when the parent is an Area2D.");
+	}
 
 	return warning;
 }
@@ -295,6 +299,7 @@ void CollisionPolygon2D::set_one_way_collision(bool p_enable) {
 	if (parent) {
 		parent->shape_owner_set_one_way_collision(owner_id, p_enable);
 	}
+	update_configuration_warning();
 }
 
 bool CollisionPolygon2D::is_one_way_collision_enabled() const {

scene/2d/collision_shape_2d.cpp

@@ -32,6 +32,7 @@
 
 #include "collision_object_2d.h"
 #include "core/engine.h"
+#include "scene/2d/area_2d.h"
 #include "scene/resources/capsule_shape_2d.h"
 #include "scene/resources/circle_shape_2d.h"
 #include "scene/resources/concave_polygon_shape_2d.h"
@@ -204,6 +205,9 @@ String CollisionShape2D::get_configuration_warning() const {
 			warning += TTR("Polygon-based shapes are not meant be used nor edited directly through the CollisionShape2D node. Please use the CollisionPolygon2D node instead.");
 		}
 	}
+	if (one_way_collision && Object::cast_to<Area2D>(get_parent())) {
+		warning += TTR("The One Way Collision property will be ignored when the parent is an Area2D.");
+	}
 
 	return warning;
 }
@@ -226,6 +230,7 @@ void CollisionShape2D::set_one_way_collision(bool p_enable) {
 	if (parent) {
 		parent->shape_owner_set_one_way_collision(owner_id, p_enable);
 	}
+	update_configuration_warning();
 }
 
 bool CollisionShape2D::is_one_way_collision_enabled() const {