Port the Azure Resource Explorer extension to core. (#2701)

* Port the Azure Resource Explorer extension to core.

This will enable Azure viewlet by default in the next release.

- Moving this code from the SQL Server 2019 extension to Azure Data Studio core
- Ported tests and verified they work in the integration tests.sh file
- Fixed an issue that caused integration tests to fail if you have a SQL Server 2019 big data cluster endpoint listed, but the extension isn't installed.

extensions/azurecore/src/azureResource/models.ts

@@ -0,0 +1,25 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the Source EULA. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+'use strict';
+
+export interface AzureResourceSubscription {
+	id: string;
+	name: string;
+}
+
+export interface AzureResourceDatabaseServer {
+	name: string;
+	fullName: string;
+	loginName: string;
+	defaultDatabaseName: string;
+}
+
+export interface AzureResourceDatabase {
+	name: string;
+	serverName: string;
+	serverFullName: string;
+	loginName: string;
+}