Wire notebook GIS widget to shared Y doc awareness

[gjmooney]

Description

This adds a getter for the newly exposed awareness so we can access it from a notebook, adds extent to the viewportState, and consolidates redundant change:center listeners.

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📚 Documentation preview: https://jupytergis--1246.org.readthedocs.build/en/1246/
💡 JupyterLite preview: https://jupytergis--1246.org.readthedocs.build/en/1246/lite
💡 Specta preview: https://jupytergis--1246.org.readthedocs.build/en/1246/lite/specta

[github-actions]

👈 Launch a Binder on branch gjmooney/jupytergis/awareness-python

[martinRenou]

@mfisher87 for context, the "awareness" is some extra transient information that we can have with collaboration.

For now, it contains information about pointer information and selected layer. I'd like us to add the viewport information, identified feature, and longer term the selected area and other goodies like this.

It's a first step towards more Python <-> JS interactions

[nakul-py]

Thanks! Greg for adding the awareness getter 🎉🎉

[martinRenou]

Thanks!