Move add_checksums_dir out of the constructor of the Shapenet dataset to fix shapenet_test.py for tensorflow_datasets version 3.1.
Move add_checksums_dir out of the constructor of the Shapenet dataset to fix shapenet_test.py for tensorflow_datasets version 3.1.

PiperOrigin-RevId: 312099499

tensorflow/graphics,tensorflow/graphics,tensorflow/graphics,tensorflow/graphics,tensorflow/graphics