**Feature or enhancement** Emit EncodingWarning in `subprocess.Popen(text=True)` and `locale.getpreferredencoding()`. **Pitch** UTF-8 Mode will affect them. So we need to emit EncodingWarning like `open()`. See [PEP 686](https://peps.python.org/pep-0686/) for detail.