[3.2] Update "Fixing type promotion failures" for private final field promo

[MaryaBelanger]

This is the work to add all the new field promotion failure anchors to the site. These are linked from context messages.

[github-actions]

Visit the preview URL for this PR (updated for commit f480d9d):

https://dart-dev--pr5246-non-promotion-ag7gz8ua.web.app

_{(expires Wed, 22 Nov 2023 18:02:06 GMT)}

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[MaryaBelanger]

Solutions for the conflict failures: I'm not sure if just renaming them is applicable when the two conflicting entities are related. Does the regular perscriptive advice apply to these three too? (i.e. create a local variable, use a null check, etc)

[stereotype441]

This is looking great Marya! I think a couple things need some additional work, but nothing major. Let me know if any of my comments aren't clear.

[stereotype441]

lgtm!

[parlough]

I haven't done a full proper review of this yet (sorry), but quickly reading through it, it looks amazing and will be a great resource for those trying to better understand type promotion failures.

I did make sure to test the links though and they all work as expected.

A few minor adjustments before landing though:

[MaryaBelanger]

Thank you Parker!