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/extension.ts

@@ -0,0 +1,40 @@
+'use strict';
+
+import * as vscode from 'vscode';
+
+import MainController from './controllers/mainController';
+import { AppContext } from './appContext';
+import ControllerBase from './controllers/controllerBase';
+import { ApiWrapper } from './apiWrapper';
+
+let controllers: ControllerBase[] = [];
+
+// this method is called when your extension is activated
+// your extension is activated the very first time the command is executed
+export function activate(extensionContext: vscode.ExtensionContext) {
+	let appContext = new AppContext(extensionContext, new ApiWrapper());
+	let activations: Promise<boolean>[] = [];
+
+	// Start the main controller
+	let mainController = new MainController(appContext);
+	controllers.push(mainController);
+	extensionContext.subscriptions.push(mainController);
+	activations.push(mainController.activate());
+
+	return Promise.all(activations)
+		.then((results: boolean[]) => {
+			for (let result of results) {
+				if (!result) {
+					return false;
+				}
+			}
+			return true;
+		});
+}
+
+// this method is called when your extension is deactivated
+export function deactivate() {
+	for (let controller of controllers) {
+		controller.deactivate();
+	}
+}