perf: don't use middleware if has build

`ember serve` and `ember test` has a `path` flag to specify
an existing ember build to use, without rebuilding. `ember-cli-typescript`
will add typechecking middleware regardless of ember using an existing
build, the typechecking middleware is not required. This can slow
down the initial request to express server significantly.

For instance one project spends 49 secs for initial typecheck on first
request.

```sh
$ DEBUG=*:* ember s --path dist
...
– Serving on http://localhost:4200/admin/
...
ember-cli-typescript:typecheck-worker Typecheck complete (0 diagnostics) +49s
...
```

Author: mrloop

ts/addon.ts

@@ -46,12 +46,16 @@ export default addon({
     return `${__dirname}/blueprints`;
   },
 
-  serverMiddleware({ app }) {
-    this._addTypecheckMiddleware(app);
+  serverMiddleware({ app, options }) {
+    if (!options?.path) {
+      this._addTypecheckMiddleware(app);
+    }
   },
 
-  testemMiddleware(app) {
-    this._addTypecheckMiddleware(app);
+  testemMiddleware(app, options) {
+    if (!options?.path) {
+      this._addTypecheckMiddleware(app);
+    }
   },
 
   async postBuild() {

ts/types/ember-cli/index.d.ts

@@ -11,6 +11,7 @@ declare module 'ember-cli/lib/models/addon' {
   import UI from 'console-ui';
   import { Application } from 'express';
   import Project from 'ember-cli/lib/models/project';
+  import { TaskOptions } from 'ember-cli/lib/models/task';
   import Command from 'ember-cli/lib/models/command';
   import EmberApp from 'ember-cli/lib/broccoli/ember-app';
   import PreprocessRegistry from 'ember-cli-preprocess-registry';
@@ -36,8 +37,8 @@ declare module 'ember-cli/lib/models/addon' {
     includedCommands(): Record<string, typeof Command | ExtendOptions<Command>> | void;
     shouldIncludeChildAddon(addon: Addon): boolean;
     isDevelopingAddon(): boolean;
-    serverMiddleware(options: { app: Application }): void | Promise<void>;
-    testemMiddleware(app: Application): void;
+    serverMiddleware(options: { app: Application; options?: TaskOptions }): void | Promise<void>;
+    testemMiddleware(app: Application, options?: TaskOptions): void;
     setupPreprocessorRegistry(type: 'self' | 'parent', registry: PreprocessRegistry): void;
   }
 }
@@ -49,6 +50,12 @@ declare module 'ember-cli/lib/models/blueprint' {
   export = Blueprint;
 }
 
+declare module 'ember-cli/lib/models/task' {
+  export interface TaskOptions {
+    path?: string;
+  }
+}
+
 declare module 'ember-cli/lib/models/command' {
   import CoreObject from 'core-object';
   import UI from 'console-ui';