google_apis: Parse start/end time for all-day events

Add support for all-day events, whose start/end time contains only a
date of format "yyyy-mm-dd." The time is assumed to be midnight UTC.

Bug: 1324197
Change-Id: I9fcff3cfafad2bc7af6365c1845a025c71cad69f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3639922
Reviewed-by: Jiaming Cheng <jiamingc@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Monica Basta <msalama@chromium.org>
Commit-Queue: Roger Tinkoff <rtinkoff@google.com>
Cr-Commit-Position: refs/heads/main@{#1003089}
NOKEYCHECK=True
GitOrigin-RevId: 6d337e643602a7708896e9fd3abd18c730b9cec6
7 files changed