chore(widget): split out graph-view.ts from docmaps-widget.ts

[andrewedstrom]

Description

This file has gotten too massive and really does like 3 things

1. be a widget
2. handle the graph view
3. Handle the details view

This PR splits the graph view responsibilities into a different file. Another PR will do the same with the details view.

Related Issues

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Checklist

• [X] I have tested these changes locally and they work as expected.
• [X] I have added or updated tests to cover any new functionality or bug fixes.
• [ ] I have updated the documentation to reflect any changes or additions to the project.
• [X] I have followed the project's code of conduct and conventions for commit messages.

Additional Information

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