Copy texture coordinates from OBJ into flex. Fixes #2464.

PiperOrigin-RevId: 732109960
Change-Id: I53438aaa1df763a28a3a401418c41782216ca5d7

Author: quagla

dm_control/mjcf/schema.xml

@@ -1137,6 +1137,7 @@
             <attribute name="point" type="string"/>
             <attribute name="element" type="string"/>
             <attribute name="texcoord" type="string"/>
+            <attribute name="facetexcoord" type="string"/>
             <attribute name="material" type="string"/>
             <attribute name="rgba" type="array" array_type="float" array_size="4"/>
             <attribute name="flatskin" type="int"/>
@@ -1503,6 +1504,7 @@
                 <attribute name="point" type="string"/>
                 <attribute name="element" type="string"/>
                 <attribute name="texcoord" type="string"/>
+                <attribute name="facetexcoord" type="string"/>
                 <attribute name="material" type="string"/>
                 <attribute name="rgba" type="array" array_type="float" array_size="4"/>
                 <attribute name="flatskin" type="int"/>
@@ -1682,6 +1684,7 @@
             <attribute name="vertex" type="array" array_type="float" array_size="5"/>
             <attribute name="element" type="float"/>
             <attribute name="texcoord" type="float"/>
+            <attribute name="facetexcoord" type="float"/>
             <attribute name="node" type="array" array_type="float" array_size="3"/>
           </attributes>
           <children>