Use device flow over PAT when we are running in a server full environment but not in a supported uri (#139255)

* initial attempt

* use github-authentication instead

* rework error handling

* update copy

* explain why Workspace

extensions/github-authentication/src/common/env.ts

@@ -0,0 +1,18 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+import { Uri } from 'vscode';
+
+const VALID_DESKTOP_CALLBACK_SCHEMES = [
+	'vscode',
+	'vscode-insiders',
+	'code-oss',
+	'vscode-wsl',
+	'vscode-exploration'
+];
+
+// This comes from the GitHub Authentication server
+export function isSupportedEnvironment(url: Uri): boolean {
+	return VALID_DESKTOP_CALLBACK_SCHEMES.includes(url.scheme) || url.authority.endsWith('vscode.dev') || url.authority.endsWith('github.dev');
+}