Expanded Snippet for API Docs

[Piinks]

Description

This PR adds 2 code snippets for the Expanded class in the API docs. The first a simple case, the second illustrating the use of the flex property.

Related Issues

Ref:#21136

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[gspencergoog]

You might consider making these into "snippet" application samples instead, using a template. That way, people could instantiate them and try them out easily.

[gspencergoog]