Docs: Review and update Generative UI docs

[edonehoo]

These docs just haven't had a general content review process yet. This will include a PR in org, but also within React and Core.

Incorporate changes made within this doc: https://docs.google.com/document/d/1rws0Qh5rY3cvzL2-fSnhiLBh55Xy5Zo7hewes9duZ2Q/edit?tab=t.0#heading=h.1dx4cuj7cl6l