Don't rely on the vscode-interactive schema for IW resources

[amunger]

necessary if we are going to use untitled resources for IW in microsoft/vscode#172974

including @debonte because of the change to getNotebookUriFromInputBoxUri, let me know if there's something I should be testing against that change.

[debonte]

let me know if there's something I should be testing against that change.

@amunger, given this executed cell:

existingVar = 1

Please verify:

1. When you type exist in the input box, you get existingVar as a completion suggestion.
2. After accepting that suggestion, ensure that your usage of existingVar (in the input box, before execution) does not have a red squiggle indicating that it is unknown / not defined.

I think that should be sufficient to verify that Pylance, Python, and Jupyter are all working together to make the IW inbox box look like a notebook cell in LSP.