Add Quickstart reference sample functionality, plus UX fixes (accessibility, data binding)

[adrastogi]

Summary of the pull request

This change adds functionality to the new Quickstart Playground feature to allow implementing extensions to show the user any reference data that went into producing the project.

References and relevant issues

Detailed description of the pull request / Additional comments

In the Quickstart Playground experimental feature, this change exposes a button that the user can click on in the user interface to view the sample directory corresponding to the closest "match" for the user's input prompt (there are supporting changes being made on the Azure extension side that pair with this change). It also includes the supporting scaffolding in the ViewModel to enable this.

As part of this change, we also fix an issue with the View retaining stale data (i.e., progress bar state and last-opened file) from the prior project generation attempt.

This change also addresses some accessibility issues:

• Added a WrapPanel for ensuring the sample prompts aren't truncated when the window is made smaller horizontally.
• Added labels for the feedback buttons
• Added labels for the Open in Visual Studio Code button
• Making the TextBlock with the generated file content a tab stop

Validation steps performed

I manually ran through the new behavior and verified that I could view the reference sample (the explorer window below was opened via the link under the Generate button).

I ran Narrator and Accessibility Insights cleanly, and visually verified the behavior of the controls that are now wrapping.

PR checklist

• Closes #xxx
• Tests added/passed
• Documentation updated