[K/N] Track object counts during sweep ^KT-55364

Previously object count was tracked via allocator. It adds additional
burden on every allocation. Tracking via sweeper is better because
it mostly happens on the GC thread during a concurrent sweep.

kotlin-native/backend.native/tests/runtime/memory/gcStats.kt

@@ -12,13 +12,11 @@ import kotlin.test.*
 @Test
 fun `nothing new collected`() {
     GC.collect()
-    GC.collect();
+    GC.collect()
     val stat = GC.lastGCInfo
     assertNotNull(stat)
-    assertEquals(stat.memoryUsageBefore.keys, stat.memoryUsageAfter.keys)
-    for (key in stat.memoryUsageBefore.keys) {
-        assertEquals(stat.memoryUsageBefore[key]!!.objectsCount, stat.memoryUsageAfter[key]!!.objectsCount)
-        assertEquals(stat.memoryUsageBefore[key]!!.totalObjectsSizeBytes, stat.memoryUsageAfter[key]!!.totalObjectsSizeBytes)
+    for (key in stat.sweepStatistics.keys) {
+        assertEquals(stat.sweepStatistics[key]!!.sweptCount, 0L)
     }
 }