SOLR-8995: Use lambdas in CoreAdminHandler

solr/core/src/java/org/apache/solr/handler/admin/CoreAdminHandler.java

@@ -362,7 +362,7 @@ public class CoreAdminHandler extends RequestHandlerBase implements PermissionNa
     }
 
     void call() throws Exception {
-      op.call(this);
+      op.execute(this);
     }
 
   }
@@ -374,7 +374,10 @@ public class CoreAdminHandler extends RequestHandlerBase implements PermissionNa
   /**
    * used by the INVOKE action of core admin handler
    */
-  public static interface Invocable {
-    public Map<String, Object> invoke(SolrQueryRequest req);
+  public interface Invocable {
+    Map<String, Object> invoke(SolrQueryRequest req);
+  }
+  interface CoreAdminOp {
+    void execute(CallInfo it) throws Exception;
   }
 }