[iceberg] Fix StatisticsFileCache JMX bean

Previously, only the cache stats were available through the JMX plugin
because only the CacheStatsMBean was exported. The file size and
column count distributions were not available. This fixes the issue by
problem by exporting the StatisticsFileCache object instead and
embedding the cache stats object

Author: ZacBlanco

presto-iceberg/src/main/java/com/facebook/presto/iceberg/IcebergCommonModule.java

@@ -195,9 +195,9 @@ public StatisticsFileCache createStatisticsFileCache(IcebergConfig config, MBean
                 .<StatisticsFileCacheKey, ColumnStatistics>weigher((key, entry) -> (int) entry.getEstimatedSize())
                 .recordStats()
                 .build();
-        CacheStatsMBean bean = new CacheStatsMBean(delegate);
-        exporter.export(generatedNameOf(StatisticsFileCache.class, connectorId), bean);
-        return new StatisticsFileCache(delegate);
+        StatisticsFileCache statisticsFileCache = new StatisticsFileCache(delegate);
+        exporter.export(generatedNameOf(StatisticsFileCache.class, connectorId), statisticsFileCache);
+        return statisticsFileCache;
     }
 
     @ForCachingHiveMetastore

presto-iceberg/src/main/java/com/facebook/presto/iceberg/statistics/StatisticsFileCache.java

@@ -14,6 +14,7 @@
 package com.facebook.presto.iceberg.statistics;
 
 import com.facebook.airlift.stats.DistributionStat;
+import com.facebook.presto.hive.CacheStatsMBean;
 import com.facebook.presto.spi.statistics.ColumnStatistics;
 import com.google.common.cache.Cache;
 import com.google.common.cache.ForwardingCache.SimpleForwardingCache;
@@ -25,10 +26,19 @@ public class StatisticsFileCache
 {
     private final DistributionStat fileSizes = new DistributionStat();
     private final DistributionStat columnCounts = new DistributionStat();
+    private final CacheStatsMBean cacheStats;
 
     public StatisticsFileCache(Cache<StatisticsFileCacheKey, ColumnStatistics> delegate)
     {
         super(delegate);
+        cacheStats = new CacheStatsMBean(delegate);
+    }
+
+    @Managed
+    @Nested
+    public CacheStatsMBean getCacheStats()
+    {
+        return cacheStats;
     }
 
     @Managed