docs: kdoc: move the core dispatch into a state table

docs: kdoc: move the core dispatch into a state table

Since all of the handlers already nicely have the same prototype, put them
into a table and call them from there and take out the extended
if-then-else series.

Reviewed-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20250606163438.229916-3-corbet@lwn.net