(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/gen-server/lib/DocApiForwarder.ts

@@ -50,6 +50,7 @@ export class DocApiForwarder {
     app.use('/api/docs/:docId/apply', withDoc);
     app.use('/api/docs/:docId/attachments', withDoc);
     app.use('/api/docs/:docId/snapshots', withDoc);
+    app.use('/api/docs/:docId/usersForViewAs', withDoc);
     app.use('/api/docs/:docId/replace', withDoc);
     app.use('/api/docs/:docId/flush', withDoc);
     app.use('/api/docs/:docId/states', withDoc);