Add support for respecting `VIRTUAL_ENV` in project commands via `--active` (#11189)
I think `UV_PROJECT_ENVIRONMENT` is too complicated for use-cases where
the user wants to sync to the active environment. I don't see a
compelling reason not to make opt-in easier. I see a lot of questions
about how to deal with this warning in the issue tracker, but it seems
painful to collect them here for posterity.
A notable behavior here — we'll treat this as equivalent to
`UV_PROJECT_ENVIRONMENT` so... if you point us to a valid virtual
environment that needs to be recreated for some reason (e.g., new Python
version request), we'll happily delete it and start over.