docs(fast-element): clean up API report surface

[janechu]

Pull Request

📖 Description

Cleans up the FAST Element API report surface by exporting and documenting public types used by the generated API, including AttributeMode literals, DOMPolicy, and FASTElementConstructor. The PR routes DOMPolicy references through the public dom-policy surface while preserving DOM subpath compatibility and regenerates the root, declarative, and hydration API reports.

📑 Test Plan

• npm run build:tsc -w @microsoft/fast-element
• npm run doc -w @microsoft/fast-element
• npm run doc:exports -w @microsoft/fast-element

✅ Checklist

General

• I have included a change request file using $ npm run change
• I have added tests for my changes.
• I have tested my changes.
• I have updated the project documentation to reflect my changes.
• I have read the CONTRIBUTING documentation and followed the standards for this project.