scripts/kernel-doc.py: properly handle struct_group macros

scripts/kernel-doc.py: properly handle struct_group macros

Handing nested parenthesis with regular expressions is not an
easy task. It is even harder with Python's re module, as it
has a limited subset of regular expressions, missing more
advanced features.

We might use instead Python regex module, but still the
regular expressions are very hard to understand. So, instead,
add a logic to properly match delimiters.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/74dee485f70b7ce85e90496bfdd360283a677a58.1744106241.git.mchehab+huawei@kernel.org