Add --watch=always option to prevent exit when stdin closes

[thecrypticace]

Fixes #9870

We were trying our best to not need an option for this but there are too many scenarios where one behavior works for a tool and the other one does not.

In general, exiting when stdin closes is still the only reliable way to guarantee a process actually exits appropriately when orphaned because the OS / kernel itself will close the file handle associated with stdin. But, in certain scenarios, stdin isn't wired up in the first place. For instance:

• Turborepo does this (or did at one point — not sure if it has been changed yet)
• Bash does this when running commands in the background ONLY when not in an interactive shell