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/appContext.ts

@@ -0,0 +1,28 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the Source EULA. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+'use strict';
+
+import * as vscode from 'vscode';
+import { ApiWrapper } from './apiWrapper';
+
+/**
+ * Global context for the application
+ */
+export class AppContext {
+
+	private serviceMap: Map<string, any> = new Map();
+	constructor(public readonly extensionContext: vscode.ExtensionContext, public readonly apiWrapper: ApiWrapper) {
+		this.apiWrapper = apiWrapper || new ApiWrapper();
+	}
+
+	public getService<T>(serviceName: string): T {
+		return this.serviceMap.get(serviceName) as T;
+	}
+
+	public registerService<T>(serviceName: string, service: T): void {
+		this.serviceMap.set(serviceName, service);
+	}
+}