Document behavior of areas with concave shapes

(cherry picked from commit be5d18163d)

doc/classes/Area.xml

@@ -4,7 +4,9 @@
 		3D area for detection and physics and audio influence.
 	</brief_description>
 	<description>
-		3D area that detects [CollisionObject] nodes overlapping, entering, or exiting. Can also alter or override local physics parameters (gravity, damping) and route audio to custom audio buses.
+		3D area that detects [CollisionObject] nodes overlapping, entering, or exiting. Can also alter or override local physics parameters (gravity, damping) and route audio to a custom audio bus.
+		To give the area its shape, add a [CollisionShape] or a [CollisionPolygon] node as a [i]direct[/i] child (or add multiple such nodes as direct children) of the area.
+		[b]Warning:[/b] See [ConcavePolygonShape] (also called "trimesh") for a warning about possibly unexpected behavior when using that shape for an area.
 	</description>
 	<tutorials>
 		<link title="3D Platformer Demo">https://godotengine.org/asset-library/asset/125</link>

doc/classes/Area2D.xml

@@ -5,6 +5,8 @@
 	</brief_description>
 	<description>
 		2D area that detects [CollisionObject2D] nodes overlapping, entering, or exiting. Can also alter or override local physics parameters (gravity, damping) and route audio to a custom audio bus.
+		To give the area its shape, add a [CollisionShape2D] or a [CollisionPolygon2D] node as a [i]direct[/i] child (or add multiple such nodes as direct children) of the area.
+		[b]Warning:[/b] See [ConcavePolygonShape2D] for a warning about possibly unexpected behavior when using that shape for an area.
 	</description>
 	<tutorials>
 		<link title="Using Area2D">$DOCS_URL/tutorials/physics/using_area_2d.html</link>

doc/classes/CollisionShape.xml

@@ -4,7 +4,8 @@
 		Node that represents collision shape data in 3D space.
 	</brief_description>
 	<description>
-		Editor facility for creating and editing collision shapes in 3D space. You can use this node to represent all sorts of collision shapes, for example, add this to an [Area] to give it a detection shape, or add it to a [PhysicsBody] to create a solid object. [b]IMPORTANT[/b]: this is an Editor-only helper to create shapes, use [method CollisionObject.shape_owner_get_shape] to get the actual shape.
+		Editor facility for creating and editing collision shapes in 3D space. Set the [member shape] property to configure the shape. [b]IMPORTANT[/b]: this is an Editor-only helper to create shapes, use [method CollisionObject.shape_owner_get_shape] to get the actual shape.
+		You can use this node to represent all sorts of collision shapes, for example, add this to an [Area] to give it a detection shape, or add it to a [PhysicsBody] to create a solid object.
 	</description>
 	<tutorials>
 		<link title="Physics introduction">$DOCS_URL/tutorials/physics/physics_introduction.html</link>

doc/classes/CollisionShape2D.xml

@@ -4,7 +4,8 @@
 		Node that represents collision shape data in 2D space.
 	</brief_description>
 	<description>
-		Editor facility for creating and editing collision shapes in 2D space. You can use this node to represent all sorts of collision shapes, for example, add this to an [Area2D] to give it a detection shape, or add it to a [PhysicsBody2D] to create a solid object. [b]IMPORTANT[/b]: this is an Editor-only helper to create shapes, use [method CollisionObject2D.shape_owner_get_shape] to get the actual shape.
+		Editor facility for creating and editing collision shapes in 2D space. Set the [member shape] property to configure the shape. [b]IMPORTANT[/b]: this is an Editor-only helper to create shapes, use [method CollisionObject2D.shape_owner_get_shape] to get the actual shape.
+		You can use this node to represent all sorts of collision shapes, for example, add this to an [Area2D] to give it a detection shape, or add it to a [PhysicsBody2D] to create a solid object.
 	</description>
 	<tutorials>
 		<link title="Physics introduction">$DOCS_URL/tutorials/physics/physics_introduction.html</link>

doc/classes/ConcavePolygonShape.xml

@@ -6,6 +6,7 @@
 	<description>
 		Concave polygon shape resource, which can be set into a [PhysicsBody] or area. This shape is created by feeding a list of triangles.
 		[b]Note:[/b] When used for collision, [ConcavePolygonShape] is intended to work with static [PhysicsBody] nodes like [StaticBody] and will not work with [KinematicBody] or [RigidBody] with a mode other than Static.
+		[b]Warning:[/b] Using this shape for an [Area] (via a [CollisionShape] node, created e.g. by using the [i]Create Trimesh Collision Sibling[/i] option in the [i]Mesh[/i] menu that appears when selecting a [MeshInstance] node) may give unexpected results: when using Godot Physics, the area will only detect collisions with the triangle faces in the [ConcavePolygonShape] (and not with any "inside" of the shape, for example), and when using Bullet Physics the area will not detect any collisions with the concave shape at all (this is a known bug).
 	</description>
 	<tutorials>
 		<link title="3D Physics Tests Demo">https://godotengine.org/asset-library/asset/675</link>

doc/classes/ConcavePolygonShape2D.xml

@@ -6,6 +6,7 @@
 	<description>
 		Concave polygon 2D shape resource for physics. It is made out of segments and is optimal for complex polygonal concave collisions. However, it is not advised to use for [RigidBody2D] nodes. A CollisionPolygon2D in convex decomposition mode (solids) or several convex objects are advised for that instead. Otherwise, a concave polygon 2D shape is better for static collisions.
 		The main difference between a [ConvexPolygonShape2D] and a [ConcavePolygonShape2D] is that a concave polygon assumes it is concave and uses a more complex method of collision detection, and a convex one forces itself to be convex in order to speed up collision detection.
+		[b]Warning:[/b] Using this shape for an [Area2D] (via a [CollisionShape2D] node) may give unexpected results: the area will only detect collisions with the segments in the [ConcavePolygonShape2D] (and not with any "inside" of the shape, for example).
 	</description>
 	<tutorials>
 	</tutorials>