Like in the hists browser, it should support folding current entry so
that it can hide unwanted details in some data structures.

The folded entries will be displayed with the '+' sign, while unfolded
entries will have the '-' sign.

Entries that have no children will not show any signs.

  Annotate type: 'struct socket' (1 samples)
        Percent     Offset       Size  Field
  -      100.00          0        128  struct socket {                                  ◆
           0.00          0          4      socket_state   state;                        ▒
           0.00          4          2      short int      type;                         ▒
           0.00          8          8      long unsigned int      flags;                ▒
           0.00         16          8      struct file*   file;                         ▒
         100.00         24          8      struct sock*   sk;                           ▒
           0.00         32          8      struct proto_ops*      ops;                  ▒
  -        0.00         64         64      struct socket_wq       wq {                  ▒
  -        0.00         64         24          wait_queue_head_t  wait {                ▒
  +        0.00         64          4              spinlock_t     lock;                 ▒
  -        0.00         72         16              struct list_head       head {        ▒
           0.00         72          8                  struct list_head*  next;         ▒
           0.00         80          8                  struct list_head*  prev;         ▒
                                                   };                                   ▒
                                               };                                       ▒
           0.00         88          8          struct fasync_struct*      fasync_list;  ▒
           0.00         96          8          long unsigned int  flags;                ▒
  +        0.00        104         16          struct callback_head       rcu;          ▒
                                           };                                           ▒
                                       };                                               ▒

This just adds the display logic for folding, actually folding action
will be implemented in the next patch.
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/20240812194447.2049187-2-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>