(core) Allow configuring (mostly hiding) various little bits of UI

Summary:
Adds two new env vars GRIST_HIDE_UI_ELEMENTS and GRIST_PAGE_TITLE_SUFFIX which translate to values in GristLoadConfig that the server sends the client when loading.

For checkin task https://gristlabs.getgrist.com/doc/check-ins/p/5#a1.s9.r1882.c19

Test Plan: Tested manually

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D3449

app/common/StringUnion.ts

@@ -33,6 +33,10 @@ export const StringUnion = <UnionType extends string>(...values: UnionType[]) =>
     return value;
   };
 
+  const checkAll = (arr: string[]): UnionType[] => {
+    return arr.map(check);
+  };
+
   /**
    * StringUnion.parse(value) returns value when it's valid, and undefined otherwise.
    */
@@ -40,6 +44,6 @@ export const StringUnion = <UnionType extends string>(...values: UnionType[]) =>
     return value != null && guard(value) ? value : undefined;
   };
 
-  const unionNamespace = {guard, check, parse, values};
+  const unionNamespace = {guard, check, parse, values, checkAll};
   return Object.freeze(unionNamespace as typeof unionNamespace & {type: UnionType});
 };

app/common/gristUrls.ts

@@ -5,6 +5,7 @@ import {encodeQueryParams, isAffirmative} from 'app/common/gutil';
 import {LocalPlugin} from 'app/common/plugin';
 import {StringUnion} from 'app/common/StringUnion';
 import {UIRowId} from 'app/common/UIRowId';
+import {getGristConfig} from 'app/common/urlUtils';
 import {Document} from 'app/common/UserAPI';
 import clone = require('lodash/clone');
 import pickBy = require('lodash/pickBy');
@@ -520,6 +521,23 @@ export interface GristLoadConfig {
   tagManagerId?: string;
 
   activation?: ActivationState;
+
+  // Parts of the UI to hide
+  hideUiElements?: IHideableUiElement[];
+
+  // String to append to the end of the HTML document.title
+  pageTitleSuffix?: string;
+}
+
+export const HideableUiElements = StringUnion("helpCenter", "billing", "templates", "multiSite", "multiAccounts");
+export type IHideableUiElement = typeof HideableUiElements.type;
+
+export function shouldHideUiElement(elem: IHideableUiElement): boolean {
+  return (getGristConfig().hideUiElements || []).includes(elem);
+}
+
+export function getPageTitleSuffix(config?: GristLoadConfig) {
+  return config?.pageTitleSuffix ?? " - Grist";
 }
 
 /**