Add built-in sphere mesh.

PiperOrigin-RevId: 791162850
Change-Id: I573a414727e79f1a495e0f2282b2faff48ab3443

test/engine/testdata/collision_convex/perf/spheremesh.xml

@@ -7,6 +7,7 @@
   </visual>
 
   <asset>
+    <mesh name="sphere" builtin="sphere" params="3" scale=".08 .08 .08"/>
     <texture type="skybox" builtin="gradient" rgb1="0.3 0.5 0.7" rgb2="0 0 0" width="64" height="64"/>
     <texture name="texplane" type="2d" builtin="checker" rgb1=".2 .3 .4" rgb2=".1 0.15 0.2" width="512" height="512" mark="cross" markrgb=".8 .8 .8"/>
     <material name="matplane" reflectance="0.3" texture="texplane" texrepeat="1 1" texuniform="true"/>
@@ -38,8 +39,4 @@
       </replicate>
     </replicate>
   </worldbody>
-
-  <asset>
-    <mesh name="sphere" builtin="wedge" params="25 25 180 90 0" scale=".08 .08 .08"/>
-  </asset>
 </mujoco>