chore(fast-html): use @microsoft/fast-build to build binding fixture

[janechu]

Uses @microsoft/fast-build to generate the index.html for the binding test fixture in @microsoft/fast-html, replacing the previously hand-authored file with a reproducible build step.

[Copilot]

Pull request overview

Updates the @microsoft/fast-html binding test fixture to be generated via @microsoft/fast-build, replacing a hand-authored index.html with an entry.html + templates.html + state.json input set and adding it to the fixture build script for reproducible regeneration.

Changes:

• Add entry.html, templates.html, and state.json inputs for the binding fixture.
• Update binding/index.html to the fast-build-generated output (including declarative shadow DOM + injected <f-template> declarations).
• Extend scripts/build-fixtures.js to build the binding fixture and add a Beachball change file.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/fast-html/test/fixtures/binding/templates.html	Adds the binding templates consumed by fast-build and injected into the generated fixture output.
packages/fast-html/test/fixtures/binding/state.json	Adds deterministic state values used to render the binding fixture at build time.
packages/fast-html/test/fixtures/binding/entry.html	Adds the fast-build entry document that references state-bound attributes for rendering.
packages/fast-html/test/fixtures/binding/index.html	Replaces the hand-authored fixture HTML with the generated output used by Playwright tests.
packages/fast-html/scripts/build-fixtures.js	Includes binding in the list of fixtures built via @microsoft/fast-build.
change/@microsoft-fast-html-binding-00c4aaaf-c636-4dc7-af40-8cd01ae1d4c9.json	Records the chore change for release tooling (type none).