[3.11] [3.12] gh-83434: Sync libregrtest and test_regrtest with the main branch (GH-117250)

[miss-islington]

• regrtest: add --bisect option to run test.bisect_cmd on failed tests #115122: Add --bisect option to regrtest (gh-115122: Add --bisect option to regrtest #115123)

• test.bisect_cmd now exit with code 0 on success, and code 1 on
  failure. Before, it was the opposite.

• test.bisect_cmd now runs the test worker process with
  -X faulthandler.

• regrtest RunTests: Add create_python_cmd() and bisect_cmd()
  methods.

(cherry picked from commit 1e5719a)

• Show number of leaks in --huntrleaks #115720: Show number of leaks in huntrleaks progress reports (gh-115720: Show number of leaks in huntrleaks progress reports #115726)

Instead of showing a dot for each iteration, show:

• '.' for zero (on negative) leaks
• number of leaks for 1-9
• 'X' if there are more leaks

This allows more rapid iteration: when bisecting, I don't need
to wait for the final report to see if the test still leaks.

Also, show the full result if there are any non-zero entries.
This shows negative entries, for the unfortunate cases where
a reference is created and cleaned up in different runs.

Test failure is still determined by the existing heuristic.

(cherry picked from commit af5f9d6)

• Running the test suite with --junit-xml and -R incorrectly reports refleaks #83434: Disable XML in regrtest when -R option is used (gh-83434: Disable XML in regrtest when -R option is used #117232)

(cherry picked from commit d52bdfb)

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(cherry picked from commit 477ef90)

Co-authored-by: Victor Stinner [email protected]
Co-authored-by: Petr Viktorin [email protected]