Project Wizard: start the selected interpreter during project init

[sharon-wang]

The interpreter selected in the Project Wizard should be the active interpreter in the newly created project window. It may take a few moments to see the interpreter selection as runtime discovery needs to complete first.

This should work for Python, R and Jupyter.

[sharon-wang]

Moved out of "Ready for Verification" since #3041 needs to be fixed first, before this is testable without workarounds.

[juliasilge]

In Positron 2024.05.0 (Universal) build 1240, the interpreter I selected is started:

new-file.mov

Note that this isn't really true as of today in the way I would expect for Python and Jupyter, because I said to make a .venv but it starts the base Python, i.e. #2838 and #2839.