Add various improvements for resource providers.

PiperOrigin-RevId: 529706437
Change-Id: I20385e031446674584349c301982dbe13b812477

src/engine/engine_resource.h

@@ -34,6 +34,12 @@ MJAPI void mju_closeResource(mjResource* resource);
 // return negative value if error
 MJAPI int mju_readResource(mjResource* resource, const void** buffer);
 
+// sets for a resource with a name partitioned as {dir}{filename}, the dir and ndir pointers
+MJAPI void mju_getResourceDir(mjResource* resource, const char** dir, int* ndir);
+
+// get directory of a file in the OS filesystem
+void mju_getfiledir(const char* filename, const char** dir, int* ndir);
+
 // read file into memory buffer (allocated here with mju_malloc)
 void* mju_fileToMemory(const char* filename, int* filesize);