docs: kdoc: extract output formatting from dump_struct()

docs: kdoc: extract output formatting from dump_struct()

The last thing done in dump_struct() is to format the structure for
printing.  That, too, is a separate activity; split it out into its own
function.

dump_struct() now fits in a single, full-hight editor screen.

Reviewed-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20250807211639.47286-12-corbet@lwn.net