Revert "test(language-service): Make project service a singleton (#39308)" (#39322)

This reverts commit 1b21350e17.

PR Close #39322

packages/language-service/ivy/test/mock_host.ts

@@ -69,12 +69,6 @@ export const host: ts.server.ServerHost = {
   },
 };
 
-/**
- * Constructing a project service is expensive (~2.5s on MacBook Pro), so it
- * should be a singleton service shared throughout all tests.
- */
-let projectService: ts.server.ProjectService;
-
 /**
  * Create a ConfiguredProject and an actual program for the test project located
  * in packages/language-service/test/project. Project creation exercises the
@@ -82,19 +76,17 @@ let projectService: ts.server.ProjectService;
  * and modify test files.
  */
 export function setup() {
-  if (!projectService) {
-    projectService = new ts.server.ProjectService({
-      host,
-      logger,
-      cancellationToken: ts.server.nullCancellationToken,
-      useSingleInferredProject: true,
-      useInferredProjectPerProjectRoot: true,
-      typingsInstaller: ts.server.nullTypingsInstaller,
-    });
-    // Opening APP_COMPONENT forces a new ConfiguredProject to be created based
-    // on the tsconfig.json in the test project.
-    projectService.openClientFile(APP_COMPONENT);
-  }
+  const projectService = new ts.server.ProjectService({
+    host,
+    logger,
+    cancellationToken: ts.server.nullCancellationToken,
+    useSingleInferredProject: true,
+    useInferredProjectPerProjectRoot: true,
+    typingsInstaller: ts.server.nullTypingsInstaller,
+  });
+  // Opening APP_COMPONENT forces a new ConfiguredProject to be created based
+  // on the tsconfig.json in the test project.
+  projectService.openClientFile(APP_COMPONENT);
   const project = projectService.findProject(TSCONFIG);
   if (!project) {
     throw new Error(`Failed to create project for ${TSCONFIG}`);