perf stat: Support inherit events during fork() for bperf

perf stat: Support inherit events during fork() for bperf

bperf has a nice ability to share PMUs, but it still does not support
inherit events during fork(), resulting in some deviations in its stat
results compared with perf.

perf stat result:
$ ./perf stat -e cycles,instructions -- ./perf test -w sqrtloop
   Performance counter stats for './perf test -w sqrtloop':

       2,316,038,116      cycles
       2,859,350,725      instructions

         1.009603637 seconds time elapsed

         1.004196000 seconds user
         0.003950000 seconds sys

bperf stat result:
$ ./perf stat --bpf-counters -e cycles,instructions -- \
      ./perf test -w sqrtloop

   Performance counter stats for './perf test -w sqrtloop':

          18,762,093      cycles
          23,487,766      instructions

         1.008913769 seconds time elapsed

         1.003248000 seconds user
         0.004069000 seconds sys

In order to support event inheritance, two new bpf programs are added
to monitor the fork and exit of tasks respectively. When a task is
created, add it to the filter map to enable counting, and reuse the
`accum_key` of its parent task to count together with the parent task.
When a task exits, remove it from the filter map to disable counting.

After support:
$ ./perf stat --bpf-counters -e cycles,instructions -- \
      ./perf test -w sqrtloop

 Performance counter stats for './perf test -w sqrtloop':

     2,316,252,189      cycles
     2,859,946,547      instructions

       1.009422314 seconds time elapsed

       1.003597000 seconds user
       0.004270000 seconds sys

Signed-off-by: Tengda Wu <wutengda@huaweicloud.com>
Cc: song@kernel.org
Cc: bpf@vger.kernel.org
Link: https://lore.kernel.org/r/20241021110201.325617-2-wutengda@huaweicloud.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>