fix: enable Quick Look AR in third-party iOS browsers without ios-src (#5188)

The AR button stopped appearing in Chrome (and Edge/Firefox/DuckDuckGo)
on iOS unless an explicit `ios-src` was provided. Those browsers can
launch Quick Look with model-viewer's auto-generated USDZ, so the
`ios-src` requirement is unnecessary and regressed behavior that worked
in 4.2.0.

Drop the `(!IS_IOS_THIRDPARTY || this.iosSrc != null)` clause from the
quick-look mode selection. Quick Look remains disabled in the Google
Search App webview (`!IS_IOS_GSA`), where it is genuinely broken.

Fixes #5185

Author: Frank3K

packages/model-viewer/src/features/ar.ts

@@ -17,7 +17,7 @@ import {property} from 'lit/decorators.js';
 import {Object3D} from 'three';
 import {USDZExporter} from 'three/examples/jsm/exporters/USDZExporter.js';
 
-import {IS_AR_QUICKLOOK_CANDIDATE, IS_IOS_GSA, IS_IOS_THIRDPARTY, IS_SCENEVIEWER_CANDIDATE, IS_WEBXR_AR_CANDIDATE} from '../constants.js';
+import {IS_AR_QUICKLOOK_CANDIDATE, IS_IOS_GSA, IS_SCENEVIEWER_CANDIDATE, IS_WEBXR_AR_CANDIDATE} from '../constants.js';
 import ModelViewerElementBase, {$needsRender, $progressTracker, $renderer, $scene, $shouldAttemptPreload, $updateSource} from '../model-viewer-base.js';
 import {enumerationDeserializer} from '../styles/deserializers.js';
 import {ARStatus, ARTracking} from '../three-components/ARRenderer.js';
@@ -244,7 +244,7 @@ configuration or device capabilities');
               break;
             }
             if (value === 'quick-look' && IS_AR_QUICKLOOK_CANDIDATE &&
-                !IS_IOS_GSA && (!IS_IOS_THIRDPARTY || this.iosSrc != null)) {
+                !IS_IOS_GSA) {
               arMode = ARMode.QUICK_LOOK;
               break;
             }