Add experimentation to Microsoft auth (#226107)

* Add experimentation to Microsoft auth

So that we can gradually roll out MSAL support.

* correct order

extensions/microsoft-authentication/src/common/experimentation.ts

@@ -0,0 +1,26 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+import * as vscode from 'vscode';
+import { getExperimentationService, IExperimentationService, IExperimentationTelemetry, TargetPopulation } from 'vscode-tas-client';
+
+export async function createExperimentationService(
+	context: vscode.ExtensionContext,
+	experimentationTelemetry: IExperimentationTelemetry,
+	isPreRelease: boolean,
+): Promise<IExperimentationService> {
+	const id = context.extension.id;
+	const version = context.extension.packageJSON['version'];
+
+	const service = getExperimentationService(
+		id,
+		version,
+		isPreRelease ? TargetPopulation.Insiders : TargetPopulation.Public,
+		experimentationTelemetry,
+		context.globalState,
+	) as unknown as IExperimentationService;
+	await service.initializePromise;
+	await service.initialFetch;
+	return service;
+}