* 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>

Inline import_helper.unload() in libregrtest.runtest to avoid one
import.

Move clear_caches() from libregrtest.refleak to libregrtest.utils to
avoid importing libregrtest.refleak when it's not needed.

clear_caches() now only calls re.purge() if 're' is in sys.modules.

Reduce the number of modules imported by libregrtest.

saved_test_environment no longer imports modules at startup, but try
to get them from sys.modules. If an module is missing, skip the test.
It also sets directly support.environment_altered.

runtest() now now two saved_test_environment instances: one before
importing the test module, one after importing it.

Remove imports from test.libregrtest.save_env:

* asyncio
* logging
* multiprocessing
* shutil
* sysconfig
* urllib.request
* warnings

When a test method imports a module (ex: warnings) and the test
has a side effect (ex: add a warnings filter), the side effect is not
detected, because the module was not imported when Python
enters the saved_test_environment context manager.

Log "Warning -- ..." test warnings into sys.__stderr__ rather than
sys.stderr, to ensure to display them even if sys.stderr is captured.

test.libregrtest.utils.print_warning() now calls
test.support.print_warning().

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.

A root cause of bpo-37936 is that it's easy to write a .gitignore
rule that's intended to apply to a specific file (e.g., the
`pyconfig.h` generated by `./configure`) but actually applies to all
similarly-named files in the tree (e.g., `PC/pyconfig.h`.)

Specifically, any rule with no non-trailing slashes is applied in an
"unrooted" way, to files anywhere in the tree.  This means that if we
write the rules in the most obvious-looking way, then

 * for specific files we want to ignore that happen to be in
   subdirectories (like `Modules/config.c`), the rule will work
   as intended, staying "rooted" to the top of the tree; but

 * when a specific file we want to ignore happens to be at the root of
   the repo (like `platform`), then the obvious rule (`platform`) will
   apply much more broadly than intended: if someone tries to add a
   file or directory named `platform` somewhere else in the tree, it
   will unexpectedly get ignored.

That's surprising behavior that can make the .gitignore file's
behavior feel finicky and unpredictable.

To avoid it, we can simply always give a rule "rooted" behavior when
that's what's intended, by systematically using leading slashes.

Further, to help make the pattern obvious when looking at the file and
minimize any need for thinking about the syntax when adding new rules:
separate the rules into one group for each type, with brief comments
identifying them.

For most of these rules it's clear whether they're meant to be rooted
or unrooted, but in a handful of cases I've only guessed.  In that
case the safer default (the choice that won't hide information) is the
narrower, rooted meaning, with a leading slash.  If for some of these
the unrooted meaning is desired after all, it'll be easy to move them
to the unrooted section at the top.

Co-Authored-By: Joannah Nanjekye <joannah.nanjekye@ibm.com>

"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.