Cleanup: use '_len' instead of '_size' w/ BLI API

- When returning the number of items in a collection use BLI_*_len()
- Keep _size() for size in bytes.
- Keep _count() for data structures that don't store length
  (hint this isn't a simple getter).

See P611 to apply instead of manually resolving conflicts.

source/blender/python/intern/bpy_operator.c

@@ -384,7 +384,7 @@ static PyObject *pyop_dir(PyObject *UNUSED(self))
 	int i;
 
 	WM_operatortype_iter(&iter);
-	list = PyList_New(BLI_ghash_size(iter.gh));
+	list = PyList_New(BLI_ghash_len(iter.gh));
 
 	for (i = 0; !BLI_ghashIterator_done(&iter); BLI_ghashIterator_step(&iter), i++) {
 		wmOperatorType *ot = BLI_ghashIterator_getValue(&iter);