Ts all the tests (#1998)

* Convert tests to TypeScript

* Add types for tests

* Rename files to TS

* Fix up test imports

* Fix TSC errors

* Liiiint

* Add types to util method signatures

* Some more types

src/common/datetime/format_date.ts

@@ -0,0 +1,20 @@
+import * as fecha from "fecha";
+
+// Check for support of native locale string options
+function toLocaleDateStringSupportsOptions() {
+  try {
+    new Date().toLocaleDateString("i");
+  } catch (e) {
+    return e.name === "RangeError";
+  }
+  return false;
+}
+
+export default (toLocaleDateStringSupportsOptions()
+  ? (dateObj: Date, locales: string) =>
+      dateObj.toLocaleDateString(locales, {
+        year: "numeric",
+        month: "long",
+        day: "numeric",
+      })
+  : (dateObj: Date) => fecha.format(dateObj, "mediumDate"));