doc(readme): replace Cordova repositories graph with Mermaid

[GitToTheHub]

GitHub Markdown has built-in functionality for creating diagrams: https://docs.github.com/en/get-started/writing-on-github/working-with-advanced-formatting/creating-diagrams#creating-mermaid-diagrams. This can be used instead of using a third party solution.

Platforms affected

Motivation and Context

Description

Testing

Checklist

• [ ] I've run the tests to see all new and existing tests pass
• [ ] I added automated test coverage as appropriate for this change
• [ ] Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• [ ] If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• [ ] I've updated the documentation if necessary