Prevent a possible double close of parent pipe fds when the subprocess
exec runs into an error.  Prevent a regular multi-close of the /dev/null
fd when any of stdin, stdout and stderr was set to DEVNULL.
news entry for subprocess double close fix.
Describe 'surrogateescape' in the documentation.

Also, improve some docstring descriptions of the 'errors' parameter.

Closes #14015.