Cleanup/refactor: BKE_libblock_alloc -> BKE_id_new in ID creation code.

Better use higher-level code from common ID management when possible.
Helps to de-duplicate logic, and reduces outside usages of more
'dangerous' functions.

Note that we could get rid of many of those `BKE_<id_type>_add`
functions now, but on the other hand several of those take extra
parameters and perform additional actions, so think we can keep them all
for now as 'non-standard ID specific creation functions'.

source/blender/blenkernel/intern/world.c

@@ -210,9 +210,7 @@ World *BKE_world_add(Main *bmain, const char *name)
 {
   World *wrld;
 
-  wrld = BKE_libblock_alloc(bmain, ID_WO, name, 0);
-
-  world_init_data(&wrld->id);
+  wrld = BKE_id_new(bmain, ID_WO, name);
 
   return wrld;
 }