screen_view is not triggered if multiple router-outlets

I'm using ion-split-pane in my project to follow master-detail pattern, in which you place two router-outlets on your app.component.html and then you can navigate separately on each side of the view. An example of this pattern is here: https://ionic-angular-v5-cduaar.stackblitz.io

I have ScreenTrackingService in providers of the app.module. When I navigate in the main router-outlet, "screen-view" and "page-view" events are fired.

```
Processing data layer push: {event: "gtm.historyChange-v2", gtm.oldUrl: "http://localhost:4200/master-1", gtm.newUrl:
"http://localhost:4200/master-2", gtm.triggers: "1_30"}

Processing GTAG command: ["event", "screen_view", { page_path: "/master-2", outlet: "primary" ...etc }]
```

When I navigate in the detail router-outlet, only "page-view" event is fired. There I can see that it has the correct url, but screen-view event is not fired.
```
Processing data layer push: {event: "gtm.historyChange-v2", gtm.oldUrl: "http://localhost:4200/detail-1", gtm.newUrl:
"http://localhost:4200/detail-2", gtm.triggers: "1_30"}
```
**Versions:**
Angular: 12.2.0
Ionic/angular: 5.7.0
firebase: 9.6.6
angular/fire: 7.2.1

首先，使用 app.module 中提供的 ScreenTrackingService 以及 app.component.html 中的兩個 outlet，在連結的 StackBlitz 中重現主從導覽。比較主要導覽和詳細導覽，並判斷為什麼只發出 page-view；當 detail-outlet 導覽以正確的 URL 發出 screen_view 時，即表示完成。

由索引模型根據 Issue 內容生成。