Make uncontrolled -> controlled warning clearer

[vcarl]

Fixes #17069. Glad to iterate further on the specific language, but I've found that explaining in this way usually clears it up for people.

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[markerikson]

I would suggest adding a sentence like "This is likely caused by value={something} changing from undefined to a defined value".

[sophiebits]

• The %s placeholder here is not the value type but rather the input type (checkbox, radio, etc). However I don’t think we need this info any more since we have robust component stacks in warnings. So let’s just remove that substitution and say “undefined value”.
• You’ll need to update any tests that are verifying this warning message.
• Other than that, this is a great improvement! Any chance you can make the above improvements? Then this can be merged.

[vcarl]

Looks like this was upgraded to an error since I opened the PR. Fixing conflicts.

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[vcarl]

No rush on this, but anything else needed for it to land? cc @sophiebits @gaearon

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This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contribution.

[gaearon]

@vcarl Sorry, there's a huge backlog and things slip through. I wanted to merge this but now the ref is gone. :-(

[vcarl]

I restored the branch, but am unsubscribing from the PR. If it lands, cool! But I'm moving on.

[gaearon]

Thanks!