include submitter value in enhanced GET forms

[eltigerchino]

fixes #8253

• Checks if a submit value is present then appends the name and value to the form data.
• Updates the enhanced GET test with an expected submit name and value pair.

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🦋 Changeset detected

Latest commit: 2a9912f368385abfbf0470d8ab6142b52862ce1c

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

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@sveltejs/kit	Patch

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[Rich-Harris]

thank you!