Add Markdown support to basic Text widget (Lit).

[ditman]

Description

Adds Markdown support to the basic Text widget of the v0_9 Lit renderer.

(This is a very similar, but separate, implementation to what exists in v0.8 today. Adds a couple of tests to the directive.)

Also modifies the demo:gallery09 to inject a Markdown renderer for testing.

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• Fixes: [Lit] Support Markdown in text Component #947

Pre-launch Checklist

• I signed the CLA.
• I read the Contributors Guide.
• I read the Style Guide.
• I have added updates to the CHANGELOG.
• I updated/added relevant documentation.
• My code changes (if any) have tests.

If you need help, consider asking for advice on the discussion board.

[gemini-code-assist]

Code Review

This pull request updates the Lit renderer to version 0.8.5, introducing markdown support for the Text widget and a new Context.markdown API for dependency injection. It adds a MarkdownDirective that utilizes unsafeHTML and until for asynchronous rendering, along with corresponding tests and sample updates. Feedback suggests improving the logic for prepending markdown heading symbols to prevent redundant formatting when the input text already contains them.

[ditman]

Should have clicked "Submit" days ago; the only change I made was to sync the changelog with the newest v0.9 version.