* Move to a static argparse.Namespace subclass
* Roughly annotate runtest.py
* Refactor libregrtest to use lossless test result objects
* Only re-run test methods that match names of previously failing test methods
* Adopt tests to cover test method name matching

Co-authored-by: Pablo Galindo Salgado <Pablogsal@gmail.com>
(cherry picked from commit f1afef5e0d93d66fbf3c9aaeab8b3b8da9617583)

Co-authored-by: Łukasz Langa <lukasz@langa.pl>

When building Python in some uncommon platforms there are some known tests that will fail. Right now, the test suite has the ability to ignore entire tests using the -x option and to receive a filter file using the --matchfile filter. The problem with the --matchfile option is that it receives a file with patterns to accept and when you want to ignore a couple of tests and subtests, is too cumbersome to lists ALL tests that are not the ones that you want to accept and he problem with -x is that is not easy to ignore just a subtests that fail and the whole test needs to be ignored.

For these reasons, add a new option to allow to ignore a list of test and subtests for these situations.

Reduce the number of unit tests run for the PGO generation task.  This
speeds up the task by a factor of about 15x.  Running the full unit test
suite is slow.  This change may result in a slightly less optimized build
since not as many code branches will be executed.  If you are willing to
wait for the much slower build, the old behavior can be restored using
'./configure [..] PROFILE_TASK="-m test --pgo-extended"'.  We make no
guarantees as to which PGO task set produces a faster build.  Users who
care should run their own relevant benchmarks as results can depend on
the environment, workload, and compiler tool chain.

* regrtest: Add --cleanup option to remove "test_python_*" directories
  of previous failed test jobs.
* Add "make cleantest" to run "python3 -m test --cleanup".

"python3 -m test -jN ..." now continues the execution of next tests
when a worker process crash (CHILD_ERROR state). Previously, the test
suite stopped immediately. Use --failfast to stop at the first error.

Moreover, --forever now also implies --failfast.

regrtest now always detects uncollectable objects. Previously, the
check was only enabled by --findleaks. The check now also works with
-jN/--multiprocess N.

--findleaks becomes a deprecated alias to --fail-env-changed.

A minor typo in the output of `python -m test -h`.
A space was missing in between two words.
howmuch -> how much