Fix malloc counters during GC

ruby#16919 changed malloc counters to be
reset in `gc_sweep_finish`. However, this introduced two problems:

1. If a GC is triggered due to the `malloc_limit` being hit, then it would
   run a GC with lazy sweeping, during lazy sweeping Ruby code could call
   `xmalloc`, which would immediately finish sweeping by calling `gc_rest`
   because the `malloc_increase` is not reset.
2. When `gc_rest` is called, it immediately completes sweeping. However,
   all of the counters for the freed memory is lost because `malloc_increase`
   is reset at the end. Previously, lazy sweeping would be interleaved
   with Ruby code execution, meaning `xfree` was interleaved with `xmalloc`,
   allowing for more memory to be allocated before `malloc_increase` hits
   `malloc_limit`.

The issue can be reproduced by this script:

   live = []
   500.times do
   live << Array.new(200) { String.new(capacity: 64 * 1024) }
   end
   puts GC.stat

Before:

   {count: 235, ..., minor_gc_count: 196, major_gc_count: 39}

After:

   {count: 196, ..., minor_gc_count: 153, major_gc_count: 43}

Author: peterzhu2118

gc/default/default.c

@@ -4023,13 +4023,6 @@ gc_sweep_finish(rb_objspace_t *objspace)
         }
     }
 
-    (void)gc_malloc_counters_snapshot(objspace, &objspace->malloc_counters.counters);
-#if RGENGC_ESTIMATE_OLDMALLOC
-    if (objspace->profile.latest_gc_info & GPR_FLAG_MAJOR_MASK) {
-        (void)gc_malloc_counters_snapshot(objspace, &objspace->malloc_counters.oldcounters);
-    }
-#endif
-
     rb_gc_event_hook(0, RUBY_INTERNAL_EVENT_GC_END_SWEEP);
     gc_mode_transition(objspace, gc_mode_none);
 
@@ -6464,6 +6457,7 @@ gc_reset_malloc_info(rb_objspace_t *objspace, bool full_mark)
     gc_prof_set_malloc_info(objspace);
     {
         int64_t inc = gc_malloc_counters_increase(objspace, &objspace->malloc_counters.counters);
+        gc_malloc_counters_snapshot(objspace, &objspace->malloc_counters.counters);
         size_t old_limit = malloc_limit;
 
         /* A net-negative `inc` (more freed than malloc'd since last GC) is
@@ -6519,6 +6513,8 @@ gc_reset_malloc_info(rb_objspace_t *objspace, bool full_mark)
                        gc_params.oldmalloc_limit_max);
     }
     else {
+        gc_malloc_counters_snapshot(objspace, &objspace->malloc_counters.oldcounters);
+
         if ((objspace->profile.latest_gc_info & GPR_FLAG_MAJOR_BY_OLDMALLOC) == 0) {
             objspace->rgengc.oldmalloc_increase_limit =
               (size_t)(objspace->rgengc.oldmalloc_increase_limit / ((gc_params.oldmalloc_limit_growth_factor - 1)/10 + 1));