Add memory utilization analytics to mallctl

The analytics tool is put under experimental.utilization namespace in
mallctl.  Input is one pointer or an array of pointers and the output
is a list of memory utilization statistics.

include/jemalloc/internal/extent_externs.h

@@ -74,4 +74,10 @@ bool extent_merge_wrapper(tsdn_t *tsdn, arena_t *arena,
 
 bool extent_boot(void);
 
+void extent_util_stats_get(tsdn_t *tsdn, const void *ptr,
+    size_t *nfree, size_t *nregs, size_t *size);
+void extent_util_stats_verbose_get(tsdn_t *tsdn, const void *ptr,
+    size_t *nfree, size_t *nregs, size_t *size,
+    size_t *bin_nfree, size_t *bin_nregs, void **slabcur_addr);
+
 #endif /* JEMALLOC_INTERNAL_EXTENT_EXTERNS_H */

include/jemalloc/internal/extent_structs.h

@@ -228,4 +228,25 @@ struct extents_s {
 	bool			delay_coalesce;
 };
 
+/*
+ * The following two structs are for experimental purposes. See
+ * experimental_utilization_query_ctl and
+ * experimental_utilization_batch_query_ctl in src/ctl.c.
+ */
+
+struct extent_util_stats_s {
+	size_t nfree;
+	size_t nregs;
+	size_t size;
+};
+
+struct extent_util_stats_verbose_s {
+	void *slabcur_addr;
+	size_t nfree;
+	size_t nregs;
+	size_t size;
+	size_t bin_nfree;
+	size_t bin_nregs;
+};
+
 #endif /* JEMALLOC_INTERNAL_EXTENT_STRUCTS_H */

include/jemalloc/internal/extent_types.h

@@ -4,6 +4,9 @@
 typedef struct extent_s extent_t;
 typedef struct extents_s extents_t;
 
+typedef struct extent_util_stats_s extent_util_stats_t;
+typedef struct extent_util_stats_verbose_s extent_util_stats_verbose_t;
+
 #define EXTENT_HOOKS_INITIALIZER	NULL
 
 /*