bpo-31756: subprocess.run should alias universal_newlines to text (#4049)

bpo-31756: subprocess.run should alias universal_newlines to text (#4049)

Improve human friendliness of the Popen API: Add text=False as a
keyword-only argument to subprocess.Popen along with a Popen
attribute .text_mode and set this based on the
encoding/errors/universal_newlines/text arguments.

The universal_newlines parameter and attribute are maintained for
backwards compatibility.