Throw an error if multiple orientation specifiers are used in the same element.

- Applies to [orientation specifiers](https://mujoco.readthedocs.io/en/latest/modeling.html#frame-orientations) in `body`, `inertial`, `geom`, `site`, `camera`.
- Before this change the check was done only for multiple *alternative* specifiers, but not for `quat` and an alternative specifier.
- Moved the check from the compiler to the parser.
- Added tests.

PiperOrigin-RevId: 453201981
Change-Id: I20907361f211dae904e734cd083e9df0efe4f654

src/xml/xml_native_reader.cc

@@ -1120,9 +1120,9 @@ void mjXReader::OneGeom(XMLElement* elem, mjCGeom* pgeom) {
   ReadAttr(elem, "mass", 1, &pgeom->_mass, text);
   ReadAttr(elem, "density", 1, &pgeom->density, text);
   ReadAttr(elem, "fromto", 6, pgeom->fromto, text);
-  ReadAlternative(elem, pgeom->alt);
   ReadAttr(elem, "pos", 3, pgeom->pos, text);
   ReadAttr(elem, "quat", 4, pgeom->quat, text);
+  ReadAlternative(elem, pgeom->alt);
 
   GetXMLPos(elem, pgeom);
 }