Expose adding files and folders in sql database projects (#14391)

* expose addToProject in dataworkspace.d.ts

* remove changes in data workspace extension

* add sqldbproj.d.ts

* change list to be Uris instead of strings

* don't add files/folders if any don't exist

* fix test on windows

extensions/sql-database-projects/src/sqldbproj.d.ts

@@ -0,0 +1,32 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the Source EULA. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+declare module 'sqldbproj' {
+	import * as vscode from 'vscode';
+	export const enum extension {
+		name = 'Microsoft.sql-database-projects'
+	}
+
+	/**
+	 * sql database projects extension
+	 */
+	export interface IExtension {
+		/**
+		 * Create a project
+		 * @param name name of the project
+		 * @param location the parent directory
+		 * @param projectTypeId the ID of the project/template
+		 * @returns Uri of the newly created project file
+		 */
+		createProject(name: string, location: vscode.Uri, projectTypeId: string): Promise<vscode.Uri>;
+
+		/**
+		* Adds the list of files and directories to the project, and saves the project file
+		* @param projectFile The Uri of the project file
+		* @param list list of uris of files and folders to add. Files and folders must already exist. No files or folders will be added if any do not exist.
+		*/
+		addToProject(projectFile: vscode.Uri, list: vscode.Uri[]): Promise<void>;
+	}
+}