This commit modifies the `rest_get_date_with_gmt` function to correctly parse local and UTC timestamps with or without timezone information.
It also ensures that the REST API can edit the dates of draft posts by setting the `edit_date` flag to `wp_update_post`.
Overall this commit ensures that post and comment dates can be set and updated as expected.
Fixes#39256.
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git-svn-id: http://core.svn.wordpress.org/trunk@40038 1a063a9b-81f0-0310-95a4-ce76da25c4cd