Revisit notebook cell uris

[jrieken]

Today, notebook cell have the following URI format

vscode-notebook-cell://<notebook-authority>/<notebook-path>, cell <handle>?<payload>

This makes then

• render in the UI like some/path/someNotebook.foo, cell 12
• makes a cell a different resource - by the rules of URI

The downsides are

• The cell handle appears in the UI and that's something users can not really relate to
• A cell is inside the notebook, not a different resource, using fragments is the better fit
• Grouping is often (but not always) bogous (see screen shot below)

The plan is to use a URI format for notebook cells that do not make them appear as separate things but make them appears as the notebook itself

[jrieken]

🧑‍🏭 work in progress 🧑‍🏭

I have changed the peek model and the references viewlet to group resources independent of their uri-fragment, e.g foo:///bar#a and foo:///bar#b are different uris pointing to the same resource. It actually works nice for those two, but I am unsure about diagnostics: there we don't show a preview but line/character, e.g. [2, 1], which only make sense in the scope of a resource. The screen shot below might be confusing because