Fix documentation: view_angles.rst, change default style

Documentation (view_angles.rst):
- Fix: only one of :: and .. code:: is needed
- Fix: :rc:`axes3d.trackballsize`/2 + :rc:`axes3d.trackballborder` does not work as a formula, use  `trackballsize/2 + trackballborder` instead
-Fix: $\sqrt 2 \approx 1.414$ now reads :math:`\sqrt 2 \approx 1.414`

matplotlibrc:
axes3d.mouserotationstyle: trackball
The style 'trackball' as default is likely to make life easier for 99% of the users who don't touch this setting (it is easiest to understand, no surprises, it works the same in the middle and at the edge of the screen, no guesswork as to how it works/what it does).

Author: MischaMegens2

doc/api/toolkits/mplot3d/view_angles.rst

@@ -129,7 +129,7 @@ Henriksen et al. [Henriksen2002]_ provide an overview. In summary:
 .. [5] The style has a corresponding natural implementation as a mechanical device
 .. [6] While it is possible to control roll with the ``trackball`` style, this is not immediately obvious (it requires moving the mouse in large circles) and a bit counterintuitive (the resulting roll is in the opposite direction)
 
-You can try out one of the various mouse rotation styles using::
+You can try out one of the various mouse rotation styles using:
 
 .. code::
 
@@ -155,9 +155,9 @@ You can try out one of the various mouse rotation styles using::
 
 Alternatively, create a file ``matplotlibrc``, with contents::
 
-    axes3d.mouserotationstyle: arcball
+    axes3d.mouserotationstyle: trackball
 
-(or any of the other styles, instead of ``arcball``), and then run any of
+(or any of the other styles, instead of ``trackball``), and then run any of
 the :ref:`mplot3d-examples-index` examples.
 
 The size of the virtual trackball, sphere, or arcball can be adjusted
@@ -177,14 +177,14 @@ originally written for OpenGL [Bell1988]_, and is used in Blender and Meshlab.
 Bell's arcball extends the arcball's spherical control surface with a hyperbola;
 the two are smoothly joined. However, the hyperbola extends all the way beyond
 the edge of the plot. In the mplot3d sphere and arcball style, the border extends
-to a radius :rc:`axes3d.trackballsize`/2 + :rc:`axes3d.trackballborder`.
+to a radius `trackballsize/2 + trackballborder`.
 Beyond the border, the style works like the original: it controls roll only.
 A border width of about 0.2 appears to work well; this is the default.
 To obtain the original Shoemake's arcball with a sharp border,
 set the border width to 0.
 For an extended border similar to Bell's arcball, where the transition from
 the arcball to the border occurs at 45°, set the border width to
-$\sqrt 2 \approx 1.414$.
+:math:`\sqrt 2 \approx 1.414`.
 
 
 .. [Shoemake1992] Ken Shoemake, "ARCBALL: A user interface for specifying

lib/matplotlib/mpl-data/matplotlibrc

@@ -433,7 +433,7 @@
 #axes3d.yaxis.panecolor:    (0.90, 0.90, 0.90, 0.5)  # background pane on 3D axes
 #axes3d.zaxis.panecolor:    (0.925, 0.925, 0.925, 0.5)  # background pane on 3D axes
 
-#axes3d.mouserotationstyle: arcball  # {azel, trackball, sphere, arcball}
+#axes3d.mouserotationstyle: trackball  # {azel, trackball, sphere, arcball}
                             # See also https://matplotlib.org/stable/api/toolkits/mplot3d/view_angles.html#rotation-with-mouse
 #axes3d.trackballsize: 0.667  # trackball diameter, in units of the Axes bbox
 #axes3d.trackballborder: 0.2  # trackball border width, in units of the Axes bbox (only for 'sphere' and 'arcball' style)