[WebAPI] Add abort reason to AbortSignal

[Rumyra]

Acceptance Criteria

• The listed features are documented sufficiently on MDN
• BCD is updated
• Interactive example and data repos are updated if appropriate
• The content has been reviewed as needed

For folks helping with Firefox related documentation

• Set bugs to dev-doc-complete
• Add entry to Firefox release notes if feature is enabled in release
  or
• Add entry to Firefox experimental features page if feature is not yet enabled in release

Features to document

https://bugzilla.mozilla.org/show_bug.cgi?id=1737771

[hamishwillee]

Status - pretty much done

As part of this need to do https://bugzilla.mozilla.org/show_bug.cgi?id=1745372

• BCD - FF97 AbortSignal has reason and throwIfAborted browser-compat-data#14418
• Docs -
  • AbortSignal.reason Adds support for AbortSignal.reason and related items #11708
  • AbortSignal.throwIfAborted - AbortSignal.throwIfAborted() - basic docs #11804
  • Additional work AbortSignal.throwIfAborted() improve examples #11907
• Release Note - FF97 AbortSignal reason/throwIfAborted release note #11805
• dev-doc-complete

Generally we need a new Using AbortController doc, but I consider that out of scope for this. Essentially right now we have one example that shows how to use it with fetch, and a bunch of little fragment examples showing just how to access bits of data. That is fine, because aborting Fetch is still the main use case.

However this is being used more widely. Further, it is reasonable for people to use this in their own APIs and in both browser and node/deno environments. As it is now, we don't explain how you would write your own code that uses controllers and exposes them for others to use. This would be a good starting point https://developers.google.com/web/updates/2017/09/abortable-fetch