scripts/kernel-doc.py: add a Python parser

Maintaining kernel-doc has been a challenge, as there aren't many
perl developers among maintainers. Also, the logic there is too
complex. Having lots of global variables and using pure functions
doesn't help.

Rewrite the script in Python, placing most global variables
inside classes. This should help maintaining the script in long
term.

It also allows a better integration with kernel-doc Sphinx
extension in the future.

I opted to keep this version as close as possible to what we
have already in Perl. There are some differences though:

1. There is one regular expression that required a rewrite:

	/\bSTRUCT_GROUP(\(((?:(?>[^)(]+)|(?1))*)\))[^;]*;/

   As this one uses two features that aren't available by the native
   Python regular expression module (re):

	- recursive patterns: ?1
	- atomic grouping (?>...)

   Rewrite it to use a much simpler regular expression:

	/\bSTRUCT_GROUP\(([^\)]+)\)[^;]*;/

   Extra care should be taken when validating this script, as such
   replacement might cause some regressions.

2. The filters are now applied only during output generation.
   In particular, "nosymbol" argument is only handled there.

   It means that, if the same file is processed twice for
   different symbols, the warnings will be duplicated.

   I opted to use this behavior as it allows the Sphinx extension
   to read the file(s) only once, and apply the filtering only
   when producing the ReST output. This hopefully will help
   to speed up doc generation

3. This version can handle multiple files and multiple directories.

   So, if one just wants to produce a big output with everything
   inside a file, this could be done with

   $ time ./scripts/kernel-doc.py -man . 2>/dev/null >new
   real    0m54.592s
   user    0m53.345s
   sys     0m0.997s

4. I tried to replicate as much as possible the same arguments
   from kernel-doc, with about the same behavior, for the
   command line parameters starting with a single dash (-parameter).

   I also added one letter aliases for each parameter, and a
   --parameter (sometimes with a better name).

5. There are some sutile nuances between how Perl handles
   certain regular expressions. In special, the qr operatior,
   which compiles a regular expression also works as a
   non-capturing group. It means that some regexes like
   this one:

	my $type1 = qr{[\w\s]+};

   needs to be mapped as:

	type1 = r'(?:[\w\s]+)?'

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/2fa671a9fb08d03a376a42d46cc0b1d3aab4ae3f.1744106241.git.mchehab+huawei@kernel.org

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