Add input to option bag for Command

[crowlKats]

Needs #11618 first.
Ref #11618 (comment)

[nayeemrmn]

From #14358 (comment), I think we should have:

export interface SpawnOptions {
  // ...
  stdin?: "piped" | "inherit" | "null" | Uint8Array;
}

I believe it should apply to spawnChild() as well.

[superboss224]

Yes, we should add it to execute commands with big input (like md5), but which have a short and simple result

[iuioiua]

#11618 has now been merged. This would be a great little feature to have!