Implement Markdown Rendering Support for Notes, Warnings, and Info in Sample App

[Arlodotexe]

Background

The sample applications for both CommunityToolkit vNext and CommunityToolkit Labs currently utilize an "Experimental" InfoBar with "Informational" severity.

Problem

The aforementioned notice is exclusively applicable to Labs components and is not removable in the Toolkit vNext sample app.

Solution

• Remove the notice from the sample app.
• Integrate the notice as a feature of the markdown renderer within the sample app. This will allow for better rendering of documents that contain elements like ![NOTE] Some information, which currently do not render as expected.
• Update existing markdown in Labs and Toolkit vNext to include the experimental InfoBar. We'll remove them from vNext when we launch stable.

This change will enhance the readability of our documentation and ensure consistent user experience across both CommunityToolkit vNext and CommunityToolkit Labs.

Open questions

Both DocFX and GitHub have their own syntax for this.

• GitHub: https://github.com/orgs/community/discussions/16925
• DocFX: https://dotnet.github.io/docfx/docs/markdown.html?tabs=linux%2Cdotnet#alerts

Which one do we want to use?

• If we use GitHub syntax, it will display on GitHub correctly, but need to be transformed to the DocFX format when we add support for that.
• If we use DocFX syntax, it won't need to be transformed before being built for DocFX, but it also won't show up right on GitHub.

[jcoc611-microsoft]

Actually DocFX and GitHub now use the same syntax, for example:

> [!WARNING]
> This is a warning

Warning

This is a warning

I implemented this in the Labs MarkdownTextBlock, will push it once the Enable/Disable built in extensions PR goes in