(core) Add tip for "Add New" button

Summary:
Adds a new tip for the doc menu's Add New button. The tip is
shown only when the current user is an editor or owner, and
the site is non-empty. The presence of welcome videos or
popups will also cause the tip to not be shown; it will instead
be shown the next time the doc menu is visited.

Test Plan: Browser tests.

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D3757

app/client/ui/WelcomeQuestions.ts

@@ -12,17 +12,15 @@ import {dom, input, Observable, styled, subscribeElem} from 'grainjs';
 
 const t = makeT('WelcomeQuestions');
 
+export function shouldShowWelcomeQuestions(userPrefsObs: Observable<UserPrefs>): boolean {
+  return Boolean(getGristConfig().survey && userPrefsObs.get()?.showNewUserQuestions);
+}
+
 /**
  * Shows a modal with welcome questions if surveying is enabled and the user hasn't
  * dismissed the modal before.
- *
- * Returns a boolean indicating whether the modal was shown or not.
  */
-export function showWelcomeQuestions(userPrefsObs: Observable<UserPrefs>): boolean {
-  if (!(getGristConfig().survey && userPrefsObs.get()?.showNewUserQuestions)) {
-    return false;
-  }
-
+export function showWelcomeQuestions(userPrefsObs: Observable<UserPrefs>) {
   saveModal((ctl, owner): ISaveModalOptions => {
     const selection = choices.map(c => Observable.create(owner, false));
     const otherText = Observable.create(owner, '');
@@ -60,8 +58,6 @@ export function showWelcomeQuestions(userPrefsObs: Observable<UserPrefs>): boole
       modalArgs: cssModalCentered.cls(''),
     };
   });
-
-  return true;
 }
 
 const choices: Array<{icon: IconName, color: string, textKey: string}> = [