Add orthographic cameras.

Orthographic cameras are specified by setting the `orthographic` attribute of the `<camera>` element. The `fovy` attribute is still used to specify the field-of-view, but its semantic is different for orthographic cameras. For orthographic cameras, the field-of-view is expressed in units of length, rather than degrees.

Other related changes:

* Fix bug in the ordering of `cam_xxx` elements in `mjModel`.
* Make camera visualization translucent only when the frustum is visualized.
* Added a button to `simulate` to toggle between perspective and orthographic free cameras.

https://youtu.be/ZXBTEIDWHhs

PiperOrigin-RevId: 642293435
Change-Id: Id090a421ad88ab404b5b27ddbbd6bfc81ad49bc5

doc/changelog.rst

@@ -13,15 +13,21 @@ General
    - Detailed documentation.
    - Python bindings.
 
-2. Added :ref:`maxhullvert<asset-mesh-maxhullvert>`, the maximum number of vertices in a mesh's convex hull.
+.. youtube:: ZXBTEIDWHhs
+   :align: right
+   :width: 240px
+
+2. Added support for orthographic cameras. This is available for both fixed cameras and the free camera, using the
+   :ref:`camera/orthographic<body-camera-orthographic>` and :ref:`global/orthographic<visual-global-orthographic>`
+   attributes, respectively.
+3. Added :ref:`maxhullvert<asset-mesh-maxhullvert>`, the maximum number of vertices in a mesh's convex hull.
 
 
 MJX
 ~~~
-
-3. Added support for :ref:`elliptic friction cones<option-cone>`.
-4. Fixed a bug that resulted in less-optimal linesearch solutions for some difficult constraint settings.
-5. Fixed a bug in the Newton solver that sometimes resulted in less-optimal gradients.
+4. Added support for :ref:`elliptic friction cones<option-cone>`.
+5. Fixed a bug that resulted in less-optimal linesearch solutions for some difficult constraint settings.
+6. Fixed a bug in the Newton solver that sometimes resulted in less-optimal gradients.
 
 Version 3.1.6 (Jun 3, 2024)
 ---------------------------