After launching an app, if successful, we connect stdio streams to it,
and wait for it to exit before we return to the prompt.
stdio is implemented as regular AppConnection messages:
- stdin: `{ $: 'stdin', data: Uint8Array }` from phoenix -> child
- stdout: `{ $: 'stdout', data: Uint8Array }` from child -> phoenix
Terminal and Phoenix now communicate with each other using the same
style, instead of 'input' and 'output' messages. This will help with
eventually running subshells.
SIGINT currently is not sent. We also suffer from the same "one more
read from stdin happens after app exits" bug that's in
PathCommandProvider where I copied the stdin code from.
This brings Phoenix's minimum required version from 20.x down to 16.x.
ReadableStream.from() is deemed experimental, and requires Node 20.x
(or at least, something higher than 18.x). This was the only code that
made us require version 20.x.
ReadableStream and WritableStream are available from Node 16.5, but
require that they be explicitly imported.