Introduce a migration guide for 3.10 new Zone error

[Hixie]

Migration guide for flutter/flutter#122836

Presubmit checklist

• This PR doesn’t contain automatically generated corrections (Grammarly or similar).
• This PR follows the Google Developer Documentation Style Guidelines — for example, it doesn’t use i.e. or e.g., and it avoids I and we (first person).
• This PR uses semantic line breaks of 80 characters or fewer.

[parlough]

Thanks for writing this document! The background and migration guide read well and make sense to me.

I noted a few issues. Could you also add a link to this doc from the breaking changes index for 3.10? https://github.com/flutter/website/blob/main/src/release/breaking-changes/index.md?plain=1#L43-L44

[github-actions]

Visit the preview URL for this PR (updated for commit bce00f0):

https://flutter-docs-prod--pr8683-hixie-patch-1-zg5b0cmh.web.app

_{(expires Tue, 30 May 2023 18:54:36 GMT)}

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[Hixie]

Could you also add a link to this doc from the breaking changes index for 3.10? https://github.com/flutter/website/blob/main/src/release/breaking-changes/index.md?plain=1#L43-L44

Done. Also fixed the missing items that were in that list.

[parlough]

Thanks! Those link definitions were mostly there by accident and weren't released yet in 3.10 or were already in the list above. I pushed fixes so that the index now matches the state of things.

[Hixie]

Thanks. I got a bit confused with the list there when doing the merge.

[parlough]

Thanks for writing this and fixing those issues. Looks good to me!

[parlough]

Thanks for writing this and fixing those issues. Looks good to me!