(core) New date filter with a calendar view

Summary:
Implements the new date filtering panel. Design results from long
discussion between: Alex, Anais, Cyprien and Dmitry.

Test environment: https://grist-new-date-range-filter.fly.dev/

Test Plan: Include various new tests.

Reviewers: georgegevoian

Reviewed By: georgegevoian

Differential Revision: https://phab.getgrist.com/D3720

app/common/getCurrentTime.ts

@@ -0,0 +1,13 @@
+import moment from "moment-timezone";
+
+/**
+ * Returns the current local time. Allows overriding via a "currentTime" URL parameter, for the sake
+ * of tests.
+ */
+export default function getCurrentTime(): moment.Moment {
+  const getDefault = () => moment();
+  if (typeof window === 'undefined' || !window) { return getDefault(); }
+  const searchParams = new URLSearchParams(window.location.search);
+
+  return searchParams.has('currentTime') ? moment(searchParams.get('currentTime')!) : getDefault();
+}