(core) Adds new view as banner

Summary:
Diff removes view-as pill in the document breadcrumbs and add new view-as banner.

Note: Banners are still missing mechanism to handle several banners. As of now both doc-usage and view-as banners could show up at the same time.

Test Plan: Refactored existing test.

Reviewers: jarek

Reviewed By: jarek

Subscribers: jarek

Differential Revision: https://phab.getgrist.com/D3732

app/client/ui/AppUI.ts

@@ -1,4 +1,5 @@
 import {buildDocumentBanners, buildHomeBanners} from 'app/client/components/Banners';
+import {ViewAsBanner} from 'app/client/components/ViewAsBanner';
 import {domAsync} from 'app/client/lib/domAsync';
 import {loadBillingPage} from 'app/client/lib/imports';
 import {createSessionObs, isBoolean, isNumber} from 'app/client/lib/sessionObs';
@@ -161,5 +162,6 @@ function pagePanelsDoc(owner: IDisposableOwner, appModel: AppModel, appObj: App)
     testId,
     contentTop: buildDocumentBanners(pageModel),
     contentBottom: dom.create(createBottomBarDoc, pageModel, leftPanelOpen, rightPanelOpen),
+    banner: dom.create(ViewAsBanner, pageModel),
   });
 }