Add ViewService interface

- Service interface with holds access to modal
  methods. To get used by views which i.e.
  want to show modal dialogs.
- Relates #825

spring-shell-core/src/main/java/org/springframework/shell/component/view/control/AbstractView.java

@@ -54,6 +54,7 @@ public abstract class AbstractView extends AbstractControl implements View {
 	private boolean hasFocus;
 	private int layer;
 	private EventLoop eventLoop;
+	private ViewService viewService;
 	private Map<Integer, KeyBindingValue> keyBindings = new HashMap<>();
 	private Map<Integer, KeyBindingValue> hotKeyBindings = new HashMap<>();
 	private Map<Integer, MouseBindingValue> mouseBindings = new HashMap<>();
@@ -238,6 +239,24 @@ public abstract class AbstractView extends AbstractControl implements View {
 		return eventLoop;
 	}
 
+	/**
+	 * Set a {@link ViewService}
+	 *
+	 * @param viewService the view service
+	 */
+	public void setViewService(ViewService viewService) {
+		this.viewService = viewService;
+	}
+
+	/**
+	 * Get a {@link ViewService}
+	 *
+	 * @return view service
+	 */
+	protected ViewService getViewService() {
+		return viewService;
+	}
+
 	protected void registerKeyBinding(Integer keyType, String keyCommand) {
 		registerKeyBinding(keyType, keyCommand, null, null);
 	}

spring-shell-core/src/main/java/org/springframework/shell/component/view/control/ViewService.java

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2023 the original author or authors.
+ *
+ * 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
+ *
+ *      https://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.springframework.shell.component.view.control;
+
+/**
+ * Provides services for a {@link View} like handling modals.
+ *
+ * @author Janne Valkealahti
+ */
+public interface ViewService {
+
+	View getModal();
+
+	void setModal(View view);
+
+}