Initial SQL Project tree viewlet in Explorer sidebar (#8639)

* Adding mock contents for tree
* added open sqlproj dialog
* reading files from directory
* Added directory traversal
* Adding tree sorting by folder vs file and label
* Improved auto-unfolding of tree based on node type
* replacing fs with fs.promise alias
* added activation event for when workspace contains sqlproj files
* Returning after displaying error

extensions/sql-database-projects/src/common/utils.ts

@@ -0,0 +1,9 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the Source EULA. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+
+export function getErrorMessage(error: Error | string): string {
+	return (error instanceof Error) ? error.message : error;
+}