DEV: dev/gdb: add simple task dump

DEV: dev/gdb: add simple task dump

New functions task_dump_wq and task_dump_rq can be used to dump tasks
in a wait queue or in a run queue respectively. For the wait queue (the
most common usage), one needs to pass either the thread-local's timers,
or the thread group ones for shared tasks:

  task_dump_wq &ha_tgroup_ctx[0].timers
  task_dump_wq &ha_thread_ctx[0].timers

For the run queue, task_dump_rq will take the thread's rqueue:

  task_dump_rq &ha_thread_ctx[0].rqueue

The output is  the task pointer and a dump of the task* struct per line,
then a total count at the end.