Embedding new diagrams for API Docs

[Piinks]

Description

This PR embeds 8 new diagrams from flutter/assets-for-api-docs:

• Container (2)
• ListView
• ListView.builder
• ListView.separated
• Align.[constant]
• Alignment
• FractionalOffset
  All of these diagrams match the sample code in the API docs for their respective class and are placed above each matching snippet.

Related Issues

Fixes #13637
Related to #21136

Checklist

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• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes tests for all changed/updated/fixed behaviors (See Test Coverage).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (flutter analyze --flutter-repo) does not report any problems on my PR.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I signed the CLA.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Does your PR require Flutter developers to manually update their apps to accommodate your change?

• No, this is not a breaking change.

[goderbauer]

LGTM with one nit

[goderbauer]

LGTM