Rewire stdio for non-interactive

[sourishkrout]

As @jlewi summarized in stateful/runme#684:

• Interactive terminals multiplex stdout and stderr and show the multiplexed stream in the Cell output window

• non-interactive terminals don't multiplex stdout/stderr and only stdout is sent to the cell output window

• non-interactive terminals don't multiple stdout & stderr because this could interfere with 3rd party renders

  • For example imagine a CLI is emitting a JSON table to stdout and also sending errors to stderr
  • If you multiple stdout & stderr you no longer have a stream of valid JSON
  • So a 3rd party renderer for JSON would break if you multiplexed stdout and stderr

• So the proposed fix for non-interactive terminals is to send stderr to the vscode integrated terminal in the bottom panel

This PR aligns the user experience with the above. Todos:

• Add/fix tests
• Test dagger integration continues to work
• Test cloud resource integration continues to work
• Finalize stderr "color" if any, it's a less alarming terminal-yellow right now

[sourishkrout]

@jlewi, here's a demo. You should be able to run it locally. Merging it still requires more work, though.

Stdio.mp4

[jlewi]

The UX looks great. One question I have for non-interactive cells, if I wanted to programmatically access stderr in order to send it to Foyle, where would I tap into it.

Consider the following example

1. We use gcloud to fetch logs from Cloud Logging
2. We use a custom renderer to render logs in a rich way
3. gcloud fails with an error because the query is wrong

In this case what I'd like to happen is

1. We send a request to Foyle with the stderr containing the error message about the logging query
2. Foyle returns a corrected command which is inserted as a ghost cell.

[sourishkrout]

I see, @jlewi. We could employ the same strategy for non-interactive, which is already being used for interactive, where we create a single output with multiple items (different media types). This is how we render Gists with serialized output whereas the notebook shows a terminal.

For interactive, we have the following:

• stateful.runme/terminal
• application/vnd.code.notebook.stdout

and for non-interactive we could probably do:

• stateful.runme/output-items
• application/vnd.code.notebook.stdout
• perhaps a third with application/vnd.code.notebook.stderr

Or combine stdout+stderr into a single application/vnd.code.notebook.stdout item.