Show database references in project tree (#10837)

* add database references to same itemgroup

* show database references in tree

* update tests

* refresh project tree after a reference is added

* addressing comments

* add validation

* Add test

* sort imports

extensions/sql-database-projects/src/models/tree/databaseReferencesTreeItem.ts

@@ -0,0 +1,37 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the Source EULA. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import * as vscode from 'vscode';
+import * as path from 'path';
+import * as constants from '../../common/constants';
+import { BaseProjectTreeItem, MessageTreeItem } from './baseTreeItem';
+import { ProjectRootTreeItem } from './projectTreeItem';
+
+/**
+ * Folder for containing references nodes in the tree
+ */
+export class DatabaseReferencesTreeItem extends BaseProjectTreeItem {
+	private references: MessageTreeItem[] = [];
+
+	constructor(project: ProjectRootTreeItem) {
+		super(vscode.Uri.file(path.join(project.uri.path, constants.databaseReferencesNodeName)), project);
+
+		this.construct();
+	}
+
+	private construct() {
+		for (const reference of (this.parent as ProjectRootTreeItem).project.databaseReferences) {
+			this.references.push(new MessageTreeItem(reference));
+		}
+	}
+
+	public get children(): BaseProjectTreeItem[] {
+		return this.references;
+	}
+
+	public get treeItem(): vscode.TreeItem {
+		return new vscode.TreeItem(this.uri, vscode.TreeItemCollapsibleState.Collapsed);
+	}
+}