ConcurrentModificationException when calling org.apache.solr.core.SolrInfoBean.getMetricsSnapshot

SOLR-11255 Updated to use  ConcurrentHashMap.newKeySet(); for all metricNames implementation but missed a few classes.

I see this exception happening once in a while:

Cause0: java.util.ConcurrentModificationException Cause0-StackTrace: at java.util.HashMap$KeySpliterator.forEachRemaining(HashMap.java:1558) at java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:580) at org.apache.solr.util.stats.MetricUtils.convertMetrics(MetricUtils.java:248) at org.apache.solr.util.stats.MetricUtils.convertMetrics(MetricUtils.java:226) at org.apache.solr.core.SolrInfoBean.getMetricsSnapshot(SolrInfoBean.java:62)

Three classes weren't updated from using a HashSet for metricNames: FastLRUCache, LFUCache and LRUCache