Use browser default time and number formatting with polyfills if needed (#9481)

Co-authored-by: Paulus Schoutsen <balloob@gmail.com>

test/common/datetime/format_date_time.ts

@@ -0,0 +1,53 @@
+import { assert } from "chai";
+
+import {
+  formatDateTime,
+  formatDateTimeWithSeconds,
+} from "../../../src/common/datetime/format_date_time";
+import { NumberFormat, TimeFormat } from "../../../src/data/translation";
+
+describe("formatDateTime", () => {
+  const dateObj = new Date(2017, 10, 18, 23, 12, 13, 400);
+
+  it("Formats English date times", () => {
+    assert.strictEqual(
+      formatDateTime(dateObj, {
+        language: "en",
+        number_format: NumberFormat.language,
+        time_format: TimeFormat.am_pm,
+      }),
+      "November 18, 2017 at 11:12 PM"
+    );
+    assert.strictEqual(
+      formatDateTime(dateObj, {
+        language: "en",
+        number_format: NumberFormat.language,
+        time_format: TimeFormat.twenty_four,
+      }),
+      "November 18, 2017 at 23:12"
+    );
+  });
+});
+
+describe("formatDateTimeWithSeconds", () => {
+  const dateObj = new Date(2017, 10, 18, 23, 12, 13, 400);
+
+  it("Formats English date times with seconds", () => {
+    assert.strictEqual(
+      formatDateTimeWithSeconds(dateObj, {
+        language: "en",
+        number_format: NumberFormat.language,
+        time_format: TimeFormat.am_pm,
+      }),
+      "November 18, 2017 at 11:12:13 PM"
+    );
+    assert.strictEqual(
+      formatDateTimeWithSeconds(dateObj, {
+        language: "en",
+        number_format: NumberFormat.language,
+        time_format: TimeFormat.twenty_four,
+      }),
+      "November 18, 2017 at 23:12:13"
+    );
+  });
+});