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_base.cc

@@ -52,9 +52,12 @@ void mjXBase::SetModel(mjCModel* _model) {
 // read alternative orientation specification
 void mjXBase::ReadAlternative(XMLElement* elem, mjCAlternative& alt) {
   string text;
-  ReadAttr(elem, "axisangle", 4, alt.axisangle, text);
-  ReadAttr(elem, "xyaxes", 6, alt.xyaxes, text);
-  ReadAttr(elem, "zaxis", 3, alt.zaxis, text);
-  ReadAttr(elem, "euler", 3, alt.euler, text);
-  ReadAttr(elem, "fullinertia", 6, alt.fullinertia, text);
+  int read = (int)(elem->Attribute("quat") != 0) +
+             (ReadAttr(elem, "axisangle", 4, alt.axisangle, text) ? 1 : 0) +
+             (ReadAttr(elem, "xyaxes", 6, alt.xyaxes, text) ? 1 : 0) +
+             (ReadAttr(elem, "zaxis", 3, alt.zaxis, text) ? 1 : 0) +
+             (ReadAttr(elem, "euler", 3, alt.euler, text) ? 1 : 0) +
+             (ReadAttr(elem, "fullinertia", 6, alt.fullinertia, text) ? 1 : 0);
+  if (read > 1)
+    throw mjXError(elem, "multiple orientation specifiers for the same field are not allowed");
 }