Change the framework switches to the new syntax
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_3880). All of your documentation changes will be reflected on that endpoint. The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_3880). All of your documentation changes will be reflected on that endpoint.
This PR updates the syntax of the framework-specific code samples. With this new syntax, you'll be able to:

- have paragraphs of text be framework-specific instead of just code samples
- have support for Flax code samples if you want.

This should be merged after https://github.com/huggingface/doc-builder/pull/63 and https://github.com/huggingface/doc-builder/pull/130