docs: kernel_include.py: append line numbers to better report errors

docs: kernel_include.py: append line numbers to better report errors

It is best to point to the original line of code that generated
an error than to point to the beginning of a directive.

Add support for it. It should be noticed that this won't work
for literal or code blocks, as Sphinx will ignore it, pointing
to the beginning of the directive. Yet, when the output is known
to be in ReST format, like on TOC, this makes the error a lot
more easier to be handled.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/a0953af8b71e64aaf2e0ba4593ad39e19587d50a.1755872208.git.mchehab+huawei@kernel.org