[3.15] gh-152132: Fix Py_RunMain() to return an exit code (GH-153446) (#153454)

[3.15] gh-152132: Fix Py_RunMain() to return an exit code (GH-153446) (#153454)

gh-152132: Fix Py_RunMain() to return an exit code (GH-153446)

* Fix Py_RunMain() to return an exit code, rather than calling
  Py_Exit(), when running a script, a command, or the REPL.
* _PyRun_SimpleFile() now logs errors to stderr, for example if setting
  __main__.__file__ fails.
* Add tests on Py_RunMain() exitcode.
* Rename functions:

  * _PyRun_SimpleStringFlagsWithName() => _PyRun_SimpleString()
  * _PyRun_SimpleFileObject() => _PyRun_SimpleFile()
  * _PyRun_AnyFileObject() => _PyRun_AnyFile()
  * _PyRun_InteractiveLoopObject() => _PyRun_InteractiveLoop()

* Change _PyRun_SimpleString(), _PyRun_SimpleFile(), _PyRun_AnyFile() and
  _PyRun_InteractiveLoop() return type to PyObject*.
* pymain_repl() now displays the error if PySys_Audit() or
  import _pyrepl failed.
* PyRun_SimpleFileExFlags() and PyRun_AnyFileExFlags() now log
  PyUnicode_DecodeFSDefault() error. So these functions can no longer
  return -1 with an exception set.
(cherry picked from commit fac72f1ee91fb380640a4c4be6df07a8f02d3110)

Co-authored-by: Victor Stinner <vstinner@python.org>