feat(amazonq): handle context command and open file for chat with lsp (aws#6999)

## Problem
for agentic chat with language server, we need client to handle open
files and update context command

## Solution


---

- Treat all work as PUBLIC. Private `feature/x` branches will not be
squash-merged at release time.
- Your code changes must meet the guidelines in
[CONTRIBUTING.md](https://github.com/aws/aws-toolkit-vscode/blob/master/CONTRIBUTING.md#guidelines).
- License: I confirm that my contribution is made under the terms of the
Apache 2.0 license.

Author: zixlin7

packages/amazonq/src/lsp/chat/messages.ts

@@ -32,6 +32,11 @@ import {
     ShowSaveFileDialogParams,
     LSPErrorCodes,
     tabBarActionRequestType,
+    ShowDocumentParams,
+    ShowDocumentResult,
+    ShowDocumentRequest,
+    contextCommandsNotificationType,
+    ContextCommandParams,
 } from '@aws/language-server-runtimes/protocol'
 import { v4 as uuidv4 } from 'uuid'
 import * as vscode from 'vscode'
@@ -286,6 +291,23 @@ export function registerMessageListeners(
             targetUri: targetUri.toString(),
         }
     })
+
+    languageClient.onRequest<ShowDocumentParams, ShowDocumentResult>(
+        ShowDocumentRequest.method,
+        async (params: ShowDocumentParams): Promise<ShowDocumentParams | ResponseError<ShowDocumentResult>> => {
+            const uri = vscode.Uri.parse(params.uri)
+            const doc = await vscode.workspace.openTextDocument(uri)
+            await vscode.window.showTextDocument(doc, { preview: false })
+            return params
+        }
+    )
+
+    languageClient.onNotification(contextCommandsNotificationType.method, (params: ContextCommandParams) => {
+        void provider.webview?.postMessage({
+            command: contextCommandsNotificationType.method,
+            params: params,
+        })
+    })
 }
 
 function isServerEvent(command: string) {

packages/amazonq/test/unit/amazonq/lsp/chat/messages.test.ts

@@ -27,6 +27,7 @@ describe('registerMessageListeners', () => {
             error: errorStub,
             sendNotification: sandbox.stub(),
             onRequest: sandbox.stub(),
+            onNotification: sandbox.stub(),
         } as unknown as LanguageClient
 
         provider = {