(core) Simple localization support and currency selector.

Summary:
- Grist document has a associated "locale" setting that affects how currency is formatted.
- Currency selector for number format.

Test Plan: not done

Reviewers: dsagal

Reviewed By: dsagal

Subscribers: paulfitz

Differential Revision: https://phab.getgrist.com/D2977

app/common/declarations.d.ts

@@ -3,3 +3,21 @@ declare module "app/common/MemBuffer" {
   type MemBuffer = any;
   export = MemBuffer;
 }
+
+declare module "locale-currency/map" {
+  const Map: Record<string, string>;
+  type Map = Record<string, string>;
+  export = Map;
+}
+
+declare namespace Intl {
+  class DisplayNames {
+    constructor(locales?: string, options?: object);
+    public of(code: string): string;
+  }
+
+  class Locale {
+    public region: string;
+    constructor(locale: string);
+  }
+}