Adds selected column component to the graph view

UI: https://screenshot.googleplex.com/4XxCChou2WW5b7p
PiperOrigin-RevId: 846195747

Author: Googler

src/app/scaffold.ng.html

@@ -1,4 +1,5 @@
 <ng-content select="ai-dag-toolbar"></ng-content>
+<ng-content select="ai-dag-shelf"></ng-content>
 <article aria-label="Graph area" i18n-aria-label="Aria label for graph area of Workflow Graph" class="flex">
   <ng-content select="ai-dag-renderer"></ng-content>
 </article>

src/app/shelf.ng.html

@@ -0,0 +1 @@
+<ng-content></ng-content>

src/app/shelf.ts

@@ -0,0 +1,33 @@
+/**
+ * @license
+ * Copyright 2022 Google LLC
+ *
+ * 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.
+ */
+
+import {ChangeDetectionStrategy, Component} from '@angular/core';
+
+/**
+ * Shelf component for DAG graph.
+ */
+@Component({
+  selector: 'ai-dag-shelf',
+  templateUrl: './shelf.ng.html',
+  changeDetection: ChangeDetectionStrategy.OnPush,
+  standalone: true,
+  host: {
+    'class': 'ai-dag-shelf',
+  },
+})
+export class AiDagShelf {
+}