fix: race condition in step functions language server activation test (aws#5244)

### Problem:
Sometimes the language server can start and fire the onReady event before we are listening for it in the tests, causing the tests to never receive the event

### Solution:
Set isReady on the ASLLanguageClient class and wait for the client to be ready in the test

Author: jpinkney-aws

packages/core/src/stepFunctions/asl/client.ts

@@ -26,7 +26,6 @@ import {
     TextEdit,
     window,
     workspace,
-    EventEmitter,
 } from 'vscode'
 
 import {
@@ -53,8 +52,7 @@ interface Settings {
 }
 
 export class ASLLanguageClient {
-    private static ASLInit = new EventEmitter<void>()
-    static onASLInit = this.ASLInit.event
+    static isReady = false
 
     /**
      * Starts the ASL LSP client/server and creates related resources (vscode `OutputChannel`,
@@ -173,7 +171,7 @@ export class ASLLanguageClient {
                     `${message}\nUse setting 'aws.stepfunctions.asl.maxItemsComputed' to configure the limit.`
                 )
             })
-            this.ASLInit.fire()
+            this.isReady = true
         })
     }
 }

packages/core/src/testInteg/stepFunctions/init.test.ts

@@ -7,6 +7,7 @@ import assert from 'assert'
 import { createTestWorkspaceFolder, openATextEditorWithText } from '../../test/testUtil'
 import vscode from 'vscode'
 import { ASLLanguageClient } from '../../stepFunctions/asl/client'
+import { waitUntil } from '../../shared'
 
 describe('stepFunctions ASL LSP', async function () {
     let tempFolder: string
@@ -23,10 +24,9 @@ describe('stepFunctions ASL LSP', async function () {
 }`
         const fileName = 'stepfunction.asl'
         const editor = await openATextEditorWithText(stateMachineFileText, fileName, tempFolder)
-        await new Promise(resolve => {
-            ASLLanguageClient.onASLInit(() => {
-                resolve(undefined)
-            })
+        await waitUntil(async () => ASLLanguageClient.isReady, {
+            timeout: 30000,
+            interval: 500,
         })
         const result = (await vscode.commands.executeCommand(
             'vscode.executeCompletionItemProvider',