Add explicit plugin method for MappedActionFilter (elastic#108515)

In preparation for elastic#108210, this commit adds a separate method to gather
MappedActionFilter instances. For now this remains compatible with the
existing getActionFilters by allowing MappedActionFilter to exist in
both places.

server/src/main/java/org/elasticsearch/action/ActionModule.java

@@ -807,6 +807,7 @@ private static ActionFilters setupActionFilters(List<ActionPlugin> actionPlugins
  finalFilters.add(filter);
  }
  }
+ mappedFilters.addAll(plugin.getMappedActionFilters());
  }
  if (mappedFilters.isEmpty() == false) {
  finalFilters.add(new MappedActionFilters(mappedFilters));

server/src/main/java/org/elasticsearch/plugins/ActionPlugin.java

@@ -15,6 +15,7 @@
 import org.elasticsearch.action.admin.indices.alias.IndicesAliasesRequest;
 import org.elasticsearch.action.admin.indices.mapping.put.PutMappingRequest;
 import org.elasticsearch.action.support.ActionFilter;
+import org.elasticsearch.action.support.MappedActionFilter;
 import org.elasticsearch.action.support.TransportAction;
 import org.elasticsearch.cluster.metadata.IndexNameExpressionResolver;
 import org.elasticsearch.cluster.node.DiscoveryNodes;
@@ -61,6 +62,13 @@ default Collection<ActionFilter> getActionFilters() {
  return Collections.emptyList();
  }
 
+ /**
+ * Action filters applying to a single action added by this plugin.
+ */
+ default Collection<MappedActionFilter> getMappedActionFilters() {
+ return Collections.emptyList();
+ }
+
  /**
  * Rest handlers added by this plugin.
  */