[3.13] gh-126925: Modify how iOS test results are gathered (GH-127592) (#127754)

Adds a `use_system_log` config item to enable stdout/stderr redirection for
Apple platforms. This log streaming is then used by a new iOS test runner
script, allowing the display of test suite output at runtime. The iOS test
runner script can be used by any Python project, not just the CPython test
suite.
(cherry picked from commit 2041a95e68ebf6d13f867e214ada28affa830669)