Update hard coded list of floating dates to use new date_floating post status arg

[TimothyBlynJacobs]

#39953 added a date_floating post status argument that clients can use to determine whether the post status is floating instead of relying on a hardcoded list.

We also need to update that hardcoded list in ​wp_insert_post() so that the post_date_gmt can be set to 0000-00-00 00:00:00 in that case as well.

[TimothyBlynJacobs]

Added a patch. Currently there is one expected unit test failure, test_create_post_as_contributor. That should be fixed when the pending post status is marked as date_floating.

[kadamwhite]

In 46279:

Posts, Post Types: Build list of "date floating" post stati dynamically when inserting post.

Completes work begun in #39953 to expose "date floating" status information to frontend clients via the REST API.

Props TimothyBlynJacobs.
Fixes #48113.

[SergeyBiryukov]

In 46318:

REST API: Use delta comparison for floating date test added in [46279] to avoid race conditions.

See #48113.