Add tokenization and context provider API types

- Implemented window delineation tests for indentation-based tokenization.
- Created tokenizer module with various tokenization strategies including TTokenizer and ApproximateTokenizer.
- Added type definitions for authentication parameters and code citation notifications.
- Introduced context provider API for extensions to supply additional context items to Copilot.
- Defined core types and schemas for position and range.
- Established status types for agent status management in IDEs.

completions-sample-code/extension/src/icon.ts

@@ -0,0 +1,11 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+export enum Icon {
+	Logo = '$(copilot)',
+	Warning = '$(copilot-warning)',
+	NotConnected = '$(copilot-not-connected)',
+	Blocked = '$(copilot-blocked)',
+}