Add mju_getXMLDependencies that given an MJCF file returns filepaths to all of it's dependencies.

PiperOrigin-RevId: 814203235
Change-Id: Ib5c2e2f4dd42224a768c88d76473544190c72bc0

test/xml/testdata/meshes/flex.obj

@@ -0,0 +1,39 @@
+# Simple Cube - OBJ File
+
+# Vertices (v)
+# 8 corners of the cube
+
+# Back Face
+v -1.0 -1.0 -1.0
+v  1.0 -1.0 -1.0
+v  1.0  1.0 -1.0
+v -1.0  1.0 -1.0
+
+# Front Face
+v -1.0 -1.0  1.0
+v  1.0 -1.0  1.0
+v  1.0  1.0  1.0
+v -1.0  1.0  1.0
+
+# Faces (f)
+# A cube has 6 faces. Each face is a quad, defined by 4 vertices.
+# The vertices are numbered according to their order of appearance above, starting from 1.
+# The order defines the face normal (front-facing) based on the right-hand rule.
+
+# Back Face (v1, v2, v3, v4)
+f 1 2 3 4
+
+# Right Face (v2, v6, v7, v3)
+f 2 6 7 3
+
+# Front Face (v5, v8, v7, v6) - Note the ordering for correct normal
+f 5 8 7 6
+
+# Left Face (v1, v4, v8, v5)
+f 1 4 8 5
+
+# Top Face (v4, v3, v7, v8)
+f 4 3 7 8
+
+# Bottom Face (v1, v5, v6, v2)
+f 1 5 6 2