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/constants.ts

@@ -0,0 +1,24 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the Source EULA. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import * as nls from 'vscode-nls';
+
+const localize = nls.loadMessageBundle();
+
+// Placeholder values
+export const dataSourcesFileName = 'datasources.json';
+
+// UI Strings
+
+export const noOpenProjectMessage = localize('noProjectOpenMessage', "No open database project");
+export const projectNodeName = localize('projectNodeName', "Database Project");
+export const dataSourcesNodeName = localize('dataSourcesNodeName', "Data Sources");
+export const foundDataSourcesFile = localize('foundDataSourcesFile', "Found {0}: ", dataSourcesFileName); // TODO: remove once datasources.json is actually getting removed.
+
+// Error messages
+
+export const multipleSqlProjFiles = localize('multipleSqlProjFilesSelected', "Multiple .sqlproj files selected; please select only one.");
+export const noSqlProjFiles = localize('noSqlProjFilesSelected', "No .sqlproj file selected; please select one.");
+export const noDataSourcesFile = localize('noDataSourcesFile', "No {0} found", dataSourcesFileName);