New FES Contributor Docs + FES Survey Link

[almchung]

This PR contains the final drafts for the new FES contributor docs + updated FES inline docs.

Changes:

• friendly_error_system.md doc is now splitted into two parts: friendly_error_system.md + fes_reference_dev_notes.md.
• friendly_error_system.md: completely re-written with a focus on the error message writing and the internationalization effort.
• friendly_error_system.md: link for FES 2021 Survey added.
• fes_reference_dev_notes.md: dev notes + technical details. The "Thoughts for Future Work" section will be updated in the next round, based on results from the FES survey (~early 2022).
• core/friendly_errors: inline docs are re-organized. Some functions' inline docs now describe their connection to the translation files. Helpful but long inline comments were moved to fes_reference_dev_notes.md.

PR Checklist

• npm run lint passes
• [Inline documentation] is included / updated
• [Unit tests] are included / updated

[almchung]

@outofambit @Qianqianye: These files are ready to be reviewed! I will also let my mentors know about this update.
Thank you so much! 🙏

[kjhollen]

Hi Alice, this looks like great progress! The main thing I'd want to see addressed before a merge is having an introduction or short technical overview of the FES functions in the contributor docs. Most other things I've noted are just questions that I have or suggestions for future work.

[almchung]

Updated reflecting feedback from @kjhollen, thank you for the great feedback!
FES Reference + Dev Notes:

1. Added an introduction paragraph
2. Swapped orders of Description and Examples sections
3. Reformatted FES output examples to have auto word-wrap
4. Fixed typos such as parameter CSS color string for _report() and _friendlyError()
5. Expanded on autoplay
6. Added items on the Future Work section: sketch_reader() and generative contributor doc

[almchung]

@Qianqianye @outofambit I'm planning to merge this by the end of the day!