Synapse query editor dropdown fix (#16684)

* formatting

* update comment

* format doc

* fix connection test

* remove unused imports

* test server info mock

* try with mocks

* add server info check for tests

* added logic for corner case

src/sql/platform/connection/common/constants.ts

@@ -32,3 +32,7 @@ export const dstsAuth = 'dstsAuth';
 export const cmsProviderName = 'MSSQL-CMS';
 
 export const UNSAVED_GROUP_ID = 'unsaved';
+
+/* Server Type Constants */
+export const sqlDataWarehouse = 'Azure SQL Data Warehouse';
+export const gen3Version = 12;