Previously, FormatDate implemented two functions:
(a) "DateTime Format Functions" as in ecma402/#sec-datetime-format-functions
(b) "FormatDateTime( dateTimeFormat, x )" as in ecma402/#sec-formatdatetime

This patch split FormatDate into two separate functions exactly as they are specified.

Cq-Include-Trybots: luci.v8.try:v8_linux_noi18n_rel_ng
Change-Id: Iae47f4d992f1767968e5a6df7d1a45a95bc33192
Reviewed-on: https://chromium-review.googlesource.com/1178886
Commit-Queue: Frank Tang <ftang@chromium.org>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55177}