feat: add browser-based MuJoCo simulation platform

wasm/web_platform/fixtures/mjcf_include/model.xml

@@ -0,0 +1 @@
+<mujoco model="fixture"><include file="world.xml"/></mujoco>

wasm/web_platform/fixtures/mjcf_include/triangle.obj

@@ -0,0 +1,8 @@
+v 0 0 0
+v 1 0 0
+v 0 1 0
+v 0 0 1
+f 1 3 2
+f 1 2 4
+f 1 4 3
+f 2 3 4

wasm/web_platform/fixtures/mjcf_include/world.xml

@@ -0,0 +1,17 @@
+<mujoco>
+  <asset>
+    <mesh name="triangle" file="triangle.obj"/>
+    <mesh name="triangle_stl" file="triangle.stl"/>
+    <texture name="checker" type="2d" file="checker.png"/>
+    <material name="checker_mat" texture="checker"/>
+  </asset>
+  <worldbody>
+    <light pos="0 0 3"/>
+    <geom type="plane" size="2 2 .1" material="checker_mat"/>
+    <body name="triangle_body" pos="0 0 1">
+      <freejoint/>
+      <geom name="triangle_geom" type="mesh" mesh="triangle" mass="1"/>
+      <geom name="stl_geom" type="mesh" mesh="triangle_stl" pos="0 0 .1" mass=".1"/>
+    </body>
+  </worldbody>
+</mujoco>