fix: avoid rebinding attr backing fields on connect

[janechu]

Pull Request

📖 Description

Fixes ElementController observable capture/rebind behavior so FAST internal backing fields, including object-valued @attr fields that have already passed through ValueConverter.fromView(), are not normalized back to public property assignments during connect().

This restores the expected behavior for converters such as JSON parsers while preserving pre-upgrade public observable capture and opt-in observer-map behavior.

🎫 Issues

• Fixes fix: ValueConverter.fromView re-invoked with already-converted value during bindObservables #7624

👩‍💻 Reviewer Notes

Please focus review on the interaction between captureBoundObservables(), bindObservables(), AttributeDefinition.setValue(), and opt-in observerMap() proxying for public own properties.

📑 Test Plan

• npm ci
• npm run build:tsc -w @microsoft/fast-element
• npm run build:rollup -w @microsoft/fast-element
• npm run build:sizes -w @microsoft/fast-element
• npm run doc -w @microsoft/fast-element
• npm run doc:exports -w @microsoft/fast-element
• npm run prebuild -w sites/website
• npx biome check packages/fast-element/src/components/element-controller.ts packages/fast-element/src/components/element-controller.pw.spec.ts packages/fast-element/src/declarative/extension-subpaths.pw.spec.ts
• npx playwright test --project=chromium src/components/element-controller.pw.spec.ts src/declarative/extension-subpaths.pw.spec.ts
• npm run checkchange
• npm run test:validation

✅ 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.

[janechu]

Marking this ready for review just to run pipelines against it.

[janechu]

For some strange reason the required Github Actions are not running against this PR, individual runs have been triggered.

Edit: unnecessary they are now passing