The BPF didn't show the per-thread stat properly.  Use task's thread id (PID)
as a key instead of stack_id and add a task_data map to save task comm names.

  $ sudo ./perf lock con -abt -E 5 sleep 1
   contended   total wait     max wait     avg wait          pid   comm

           1    740.66 ms    740.66 ms    740.66 ms         1950   nv_queue
           3    305.50 ms    298.19 ms    101.83 ms         1884   nvidia-modeset/
           1     25.14 us     25.14 us     25.14 us      2725038   EventManager_De
          12     23.09 us      9.30 us      1.92 us            0   swapper
           1     20.18 us     20.18 us     20.18 us      2725033   EventManager_De
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Blake Jones <blakejones@google.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <song@kernel.org>
Cc: bpf@vger.kernel.org
Link: https://lore.kernel.org/r/20221209190727.759804-3-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>