This commit improves docs of the front-matter module.
Specifically, the following things are done:
- Use `@example` where appropriate to render the examples more beautifully
- Split the big example attached to `createExtractor` function into smaller pieces so that each one has minimal yet meaningful example
- Add `@returns` to the `test` function
- Deduplicate `Format` type definition
- Add a brief description to `Format` type
Towards #3764
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Co-authored-by: Asher Gomez <ashersaupingomez@gmail.com>
