Prevent accidental changes of default values (#29528)

The default percentiles values and the default highlighter per- and
post-tags are currently publicly accessible and can be altered any time.
This change prevents this by restricting field access.

server/src/main/java/org/elasticsearch/search/aggregations/metrics/percentiles/PercentilesAggregationBuilder.java

@@ -26,7 +26,6 @@ import org.elasticsearch.common.xcontent.ObjectParser;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentParser;
 import org.elasticsearch.search.aggregations.AggregationBuilder;
-import org.elasticsearch.search.aggregations.AggregatorFactories;
 import org.elasticsearch.search.aggregations.AggregatorFactories.Builder;
 import org.elasticsearch.search.aggregations.AggregatorFactory;
 import org.elasticsearch.search.aggregations.metrics.percentiles.hdr.HDRPercentilesAggregatorFactory;
@@ -50,7 +49,7 @@ import java.util.function.Consumer;
 public class PercentilesAggregationBuilder extends LeafOnly<ValuesSource.Numeric, PercentilesAggregationBuilder> {
     public static final String NAME = Percentiles.TYPE_NAME;
 
-    public static final double[] DEFAULT_PERCENTS = new double[] { 1, 5, 25, 50, 75, 95, 99 };
+    private static final double[] DEFAULT_PERCENTS = new double[] { 1, 5, 25, 50, 75, 95, 99 };
     public static final ParseField PERCENTS_FIELD = new ParseField("percents");
     public static final ParseField KEYED_FIELD = new ParseField("keyed");
     public static final ParseField METHOD_FIELD = new ParseField("method");

server/src/main/java/org/elasticsearch/search/fetch/subphase/highlight/HighlightBuilder.java

@@ -75,9 +75,9 @@ public class HighlightBuilder extends AbstractHighlighterBuilder<HighlightBuilde
     /** the default number of fragments size in characters */
     public static final int DEFAULT_FRAGMENT_CHAR_SIZE = 100;
     /** the default opening tag  */
-    public static final String[] DEFAULT_PRE_TAGS = new String[]{"<em>"};
+    static final String[] DEFAULT_PRE_TAGS = new String[]{"<em>"};
     /** the default closing tag  */
-    public static final String[] DEFAULT_POST_TAGS = new String[]{"</em>"};
+    static final String[] DEFAULT_POST_TAGS = new String[]{"</em>"};
 
     /** the default opening tags when <tt>tag_schema = "styled"</tt>  */
     public static final String[] DEFAULT_STYLED_PRE_TAG = {