`@std/cli`: move informational output to `stderr` (instead of `stdout`)

Refer to the comments beginning here for context: https://github.com/denoland/std/issues/5002#issuecomment-2181247050

It appears that some modules (e.g. [`spinner.ts`](https://github.com/denoland/std/blob/release-2024.07.19/cli/spinner.ts) and [`prompt_secret.ts`](https://github.com/denoland/std/blob/release-2024.07.19/cli/prompt_secret.ts), but there may be more) are still writing informational output to `stdout`. Is this really the intended behavior?