docs: add a simple kdoc-test.yaml together with a validation tool

docs: add a simple kdoc-test.yaml together with a validation tool

Create a simple kdoc-test.yaml to be used to create unit tests for
kernel-doc parser and output classes.

For now, all we want is a simple function mapped on a yaml test
using the defined schema.

To be sure that the schema is followed, add an unittest for
the file, which will also validate that the schema is properly
parsed.

It should be noticed that the .TH definition for the man format
contains a timestamp. We'll need to handle that when dealing with
the actual implementation for the ManOutput class unit tests.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <74883976348c964f00161696d525c33ddd8c7641.1773823995.git.mchehab+huawei@kernel.org>