Add support for printing to stdout in mj_saveLastXML.

PiperOrigin-RevId: 546849864
Change-Id: I799ea3fcd723cf036f82ef5c1ef8152c314072dc

src/xml/xml.h

@@ -23,7 +23,7 @@
 // Top level API
 
 // Main writer function
-bool mjWriteXML(mjCModel* model, std::string filename, char* error, int error_sz);
+std::string mjWriteXML(mjCModel* model, char* error, int error_sz);
 
 // Main parser function
 mjCModel* mjParseXML(const char* filename, int vfs_provider, char* error, int error_sz);