bpo-34812: subprocess._args_from_interpreter_flags(): add isolated (GH-10675) (GH...

bpo-34812: subprocess._args_from_interpreter_flags(): add isolated (GH-10675) (GH-10688)

The "-I" command line option (run Python in isolated mode) and -X
options (like -X faulthandler) are now also copied by the
multiprocessing and distutils modules when spawning child processes.
Previously, only -E and -s options (enabled by -I) were copied.

subprocess._args_from_interpreter_flags() now copies the -I flag
and options from sys._xoptions like -X dev.

(cherry picked from commit 9de363271519e0616f4a7b59427057c4810d3acc)