ref-manual: Suggested fleshing out of the sigdata/siginfo documentation

ref-manual: Suggested fleshing out of the sigdata/siginfo documentation

Fixes [YOCTO #10141]

Provided several fixes to address this situation:

 * Renamed "Debugging Build Failures" to "Debugging Tools and
   Techniques" as it fit better the subsections.

 * Renamed "Viewing Dependencies" to "Viewing Dependencies
   Between Recipes and Tasks" as it fit better the description.

 * Added a new "Viewing Task Variable Dependencies" section
   to describe how sigdata and siginfo stuff can be used.

 * Replaced the contents of "4.3.4.1 Debugging" with a shorter
   bit that now references into the new section on veiwing
   task variable dependencies.

(From yocto-docs rev: 539d76366055bed74ccc926519e969324cac470d)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>