Closes #7985

Describe your changes:

This feature adds an error message option for every form control created via the Forms API. Error message display is initiated via a form control's validate function. The function's second parameter is a function through which an error message may be passed. For example:

function validate(data, fail) { return fail("My error message."); }

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• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Is this a notable change that will require a special callout in the release notes? For example, will this break compatibility with existing APIs or projects that consume these plugins?

Author Checklist

• Changes address original issue?
• Tests included and/or updated with changes?
• Has this been smoke tested?
• Have you associated this PR with a type: label? Note: this is not necessarily the same as the original issue.
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• Testing instructions included in associated issue OR is this a dependency/testcase change?

Reviewer Checklist

• Changes appear to address issue?
• Reviewer has tested changes by following the provided instructions?
• Changes appear not to be breaking changes?
• Appropriate automated tests included?
• Code style and in-line documentation are appropriate?

Testing Instructions

1. In the action menu, click "Import From JSON"
2. For the file input, select a non-JSON text file.
3. Upon failed validation, the associated error message will appear in the form under the control.