[3.14] gh-133653: Fix argparse.ArgumentParser with the formatter_class argument (GH-133813)

[miss-islington]

• Fix TypeError when formatter_class is a custom subclass of
  HelpFormatter.
• Fix TypeError when formatter_class is not a subclass of
  HelpFormatter and non-standard prefix_char is used.
• Fix support of colorizing when formatter_class is not a subclass of
  HelpFormatter.
• Remove the prefix_chars parameter of HelpFormatter.
  (cherry picked from commit 734e15b)

Co-authored-by: Serhiy Storchaka [email protected]

• Issue: argparse.HelpFormatter subclasses may be broken by 3.14 changes #133653