Fix confusing SliderJoint3D brief description

(cherry picked from commit 27f964d5380134c6384cd2cc1331f0db7b46d755)

doc/classes/ConeTwistJoint.xml

@@ -1,12 +1,12 @@
 <?xml version="1.0" encoding="UTF-8" ?>
 <class name="ConeTwistJoint" inherits="Joint" version="3.2">
 	<brief_description>
-		A twist joint between two 3D bodies.
+		A twist joint between two 3D PhysicsBodies.
 	</brief_description>
 	<description>
 		The joint can rotate the bodies across an axis defined by the local x-axes of the [Joint].
 		The twist axis is initiated as the X axis of the [Joint].
-		Once the Bodies swing, the twist axis is calculated as the middle of the x-axes of the Joint in the local space of the two Bodies.
+		Once the Bodies swing, the twist axis is calculated as the middle of the x-axes of the Joint in the local space of the two Bodies. See also [Generic6DOFJoint].
 	</description>
 	<tutorials>
 	</tutorials>

doc/classes/HingeJoint.xml

@@ -1,10 +1,10 @@
 <?xml version="1.0" encoding="UTF-8" ?>
 <class name="HingeJoint" inherits="Joint" version="3.2">
 	<brief_description>
-		A hinge between two 3D bodies.
+		A hinge between two 3D PhysicsBodies.
 	</brief_description>
 	<description>
-		A HingeJoint normally uses the Z axis of body A as the hinge axis, another axis can be specified when adding it manually though.
+		A HingeJoint normally uses the Z axis of body A as the hinge axis, another axis can be specified when adding it manually though. See also [Generic6DOFJoint].
 	</description>
 	<tutorials>
 	</tutorials>

doc/classes/PinJoint.xml

@@ -1,10 +1,10 @@
 <?xml version="1.0" encoding="UTF-8" ?>
 <class name="PinJoint" inherits="Joint" version="3.2">
 	<brief_description>
-		Pin joint for 3D shapes.
+		Pin joint for 3D PhysicsBodies.
 	</brief_description>
 	<description>
-		Pin joint for 3D rigid bodies. It pins 2 bodies (rigid or static) together.
+		Pin joint for 3D rigid bodies. It pins 2 bodies (rigid or static) together. See also [Generic6DOFJoint].
 	</description>
 	<tutorials>
 	</tutorials>

doc/classes/SliderJoint.xml

@@ -1,10 +1,10 @@
 <?xml version="1.0" encoding="UTF-8" ?>
 <class name="SliderJoint" inherits="Joint" version="3.2">
 	<brief_description>
-		Piston kind of slider between two bodies in 3D.
+		Slider between two PhysicsBodies in 3D.
 	</brief_description>
 	<description>
-		Slides across the X axis of the pivot object.
+		Slides across the X axis of the pivot object. See also [Generic6DOFJoint].
 	</description>
 	<tutorials>
 	</tutorials>