Update re-thrown error for incompatible Java/Gradle versions to include migration guide

[camsim99]

Updates error message concerning incompatible Java/Gradle versions to reference migration guide that will be created in flutter/website#8501.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
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• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
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[gmackall]

This LGTM if we are of the opinion that the info should only be on the migration guide.

I do somewhat think that there is value to leaving the existing steps, and then providing the link as a "for more info, see:" type of link. It can be a nicer experience to just see the answer, instead of having to copy a link and open it in a browser. But also understand if we want all the info in one place, instead of multiple.

[camsim99]

This LGTM if we are of the opinion that the info should only be on the migration guide.

I do somewhat think that there is value to leaving the existing steps, and then providing the link as a "for more info, see:" type of link. It can be a nicer experience to just see the answer, instead of having to copy a link and open it in a browser. But also understand if we want all the info in one place, instead of multiple.

I thought the same thing, but didn't want to be redundant. The current steps are definitely more vague than the guide, and the guide should include the information I had before. Deferring to @mariamhas and @reidbaker

[mariamhas]

Gray you make a valid point on making it easier for developers, but if the steps are not robust enough or complete they might confuse the developer and end up making things more difficult. I think its better to keep the instructions in one place as source of truth for when we eventually have to update them again, itll be easier to do it in one place than several.

[gmackall]

Gray you make a valid point on making it easier for developers, but if the steps are not robust enough or complete they might confuse the developer and end up making things more difficult. I think its better to keep the instructions in one place as source of truth for when we eventually have to update them again, itll be easier to do it in one place than several.

Sure, that makes sense! This LGTM then