Add default behavior for padded_shapes.
Add default behavior for padded_shapes.

With this change default behavior is: any unknown-dimension in a component's shape is padded to the maximum of the batch.

An error is raised if any component has an unknown rank.

No backwards compatibility concerns: this just allows you to call `.padded_batch` without passing `padded_shapes`

PiperOrigin-RevId: 288315115

tensorflow/docs-l10n