perf hist: Allow custom output fields in hierarchy mode

perf hist: Allow custom output fields in hierarchy mode

Now it can handle multiple output fields and sort keys in separate
levels, so it should be ok to use it in the hierarchy mode.  This
allows fully customized output format.

  $ perf report -F latency,comm,parallelism -H --stdio
  ...
  #     Latency  Command / Parallelism
  # ...........  .....................
  #
      31.84%     cc1
         29.96%     5
          1.24%     4
          0.37%     6
          0.26%     3
          0.02%     2
      24.68%     as
         22.39%     5
          1.12%     2
          0.98%     4
          0.12%     3
          0.07%     6
          ...

Committer testing:

Before:

  $ perf report -F latency,comm,parallelism -H --stdio
  Error: --hierarchy and --fields options cannot be used together

   Usage: perf report [<options>]

      -F, --fields <key[,keys...]>
                            output field(s): overhead latency overhead_sys overhead_us
  			  overhead_guest_sys overhead_guest_us overhead_children
  			  latency_children sample period weight1 weight2 weight3
  <SNIP>
      -H, --hierarchy       Show entries in a hierarchy
  $

After:

  $ perf report -F latency,comm,parallelism -H --stdio
  # Total Lost Samples: 0
  #
  # Samples: 1K of event 'cycles:Pu'
  # Event count (approx.): 1581450138
  #
  #     Latency  Command / Parallelism
  # ...........  .....................
  #
      97.66%     git
         96.95%     1
          0.55%     2
          0.04%     5
          0.03%     8
          0.03%     4
          0.02%     3
          0.01%     9
          0.01%     7
          0.01%     6
          0.01%     10
          0.00%     12
       2.34%     git-remote-http
          2.24%     1
          0.07%     5
          0.02%     2
          0.00%     4

  #
  # (Tip: To analyze particular parallelism levels, try: perf report --latency --parallelism=32-64)

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250331073722.4695-5-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>