[Data] Add inverse transform functionality to LabelEncoder

[samhallam-reverb]

Why are these changes needed?

This adds an inverse_transform method to the LabelEncoder class, inspired by similar functionality in scikit-learn.

Related issue number

Checks

• I've signed off every commit(by using the -s flag, i.e., git commit -s) in this PR.
• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
  • I've added any new APIs to the API Reference. For example, if I added a
    method in Tune, I've added it in doc/source/tune/api/ under the
    corresponding .rst file.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested :(

[bveeramani]

Thanks! Overall looks good. Just left some minor comments

[stale]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed in 14 days if no further activity occurs. Thank you for your contributions.

• If you'd like to keep this open, just leave any comment, and the stale label will be removed.

[github-actions]

Attention: External code changed

A previous version of this PR changed code that is used or cited in external sources, e.g. blog posts.

It looks like these changes have been reverted or are otherwise not present in this PR anymore. Please still carefully review the changes to make sure code we use in external sources still works.

[bveeramani]

LGTM! Thank you!