Added mechanism for apps to easily add their own custom link/node/host highlighting wihout having to create a new UI extensions

Change-Id: Iefa21d76190c60db79a4b07a8b22e301d29fe58e
diff --git a/core/api/src/main/java/org/onosproject/ui/UiTopoHighlighterFactory.java b/core/api/src/main/java/org/onosproject/ui/UiTopoHighlighterFactory.java
new file mode 100644
index 0000000..8a2d976
--- /dev/null
+++ b/core/api/src/main/java/org/onosproject/ui/UiTopoHighlighterFactory.java
@@ -0,0 +1,30 @@
+/*
+ * Copyright 2021-present Open Networking Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.ui;
+
+/**
+ * Abstraction of an entity capable of producing a a new topology highlighter.
+ */
+public interface UiTopoHighlighterFactory {
+
+    /**
+     * Produces a new topology highlighter.
+     *
+     * @return newly created topology highlighter
+     */
+    UiTopoHighlighter newTopoHighlighter();
+
+}