docs: kdoc: rework the handling of SPECIAL_SECTION

docs: kdoc: rework the handling of SPECIAL_SECTION

Move the recognition of this state to when we enter it, rather than when we
exit, eliminating some twisty logic along the way.

Some changes in output do result from this shift, generally for kerneldoc
comments that do not quite fit the format.  See, for example,
struct irqdomain.  As far as I can tell, the new behavior is more correct
in each case.

Reviewed-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20250621203512.223189-7-corbet@lwn.net