Evaluate using `CloseableContext` in other components than `Dialog`

[lyzadanger]

https://github.com/hypothesis/frontend-shared/releases/tag/v6.5.0 adds a CloseableContext to the Dialog component, which allows nested components to access a close handler. We might consider adding a CloseableContext to other components that are inherently "close-able", such as Panel or ModalDialog.