Spring clean bedrock documentation

[alexgibson]

Description

There's quite a lot of different pages in the bedrock docs that have been changed incrementally over time. It would be nice to take a high level pass over the documentation as a whole to try and fix some low hanging fruit:

• Could the overall structure be organised in a better way that makes things easier to find?
• Fix typos / broken links (link rot etc).
• Fix any formatting errors where info is not displayed correctly.
• Remove outdated or obsolete information.

---

Success Criteria

• Existing documentation is audited for the above.

[maureenlholland]

Re: broken links, before I forget about it, want to note "system path" 404

https://bedrock.readthedocs.io/en/latest/testing.html#running-functional-tests:
To run the tests using Firefox, you must also first download geckodriver and make it available in your system path.

More broken links:
https://bedrock.readthedocs.io/en/latest/testing.html#running-jasmine-tests-using-karma
broken: https://jasmine.github.io/1.3/introduction.html

https://bedrock.readthedocs.io/en/latest/testing.html#headless-tests
broken: https://github.com/mozilla/bedrock/blob/main/tests/functional/test_download_l10n.py

broken: https://bedrock.readthedocs.io/en/latest/stub-attribution.html (must be a leftover reference somewhere before the page was called /firefox-stub-attribution)

[reemhamz]

I think it would be a good idea to start meshing information in some parts of the documentation with how we handle things in their Protocol macro counterparts. For example, it took me and Maureen a bit to see how to use l10n_img helper with Protocol macros. I was personally referencing the helper's section in the docs. I couldn't find any macro utilizing that helper in our codebase and kept getting different errors trying out different syntax for using the helper. We then came to realize it was a boolean parameter macros and figured it out from there.

Though I could have scoured the appropriate part of docs first-thing (l10n_img is mentioned as a boolean here https://bedrock.readthedocs.io/en/latest/coding.html#split), it would have been a little less work if the l10n_img subsection just quickly mentioned how we handled things in our macros.
It would just be a nicer idea to create less friction when referincing how some helpers are used under their main/respective section in the docs, especially since macros are very heavily used in Bedrock now :)