Post date should not be updated when post is set "pending review"

[davisshaver]

A newsroom user reported the following:

Can we make the default publish date “immediately” like it was before the site update? Still having some issues with accidentally backdating, taking too long to change the date/time when publishing breaking news, etc.

After investigation, I described the issue as seen above: The post date should not be set when post is "pending review". The newsroom user agreed with this assessment.

Publishing a post from draft is immediately but the other statuses we use regularly (pending, proofed, reserve) the post date gets set

Here is a GIF demonstrating this behavior, which I believe constitutes a "bug" since the behavior is different than what happened in the same situation pre-Gutenberg.

This issue seems related to #7195 and solution #9967. cc @kadamwhite @earnjam @tofumatt who participated on the original thread.

[earnjam]

Ah, that's because it's only looking at status of draft or auto-draft. We'll need to account for pending also.

[earnjam]

Thinking about this a bit more, this does highlight that we can't fully support floating dates and custom post statuses with the hackish solution we're using of comparing the two date values + post status.

Just adding pending like I've done in #13178 won't fix the issue for proofed and reserve mentioned in the original issue. Technically custom post statuses aren't officially supported by core, but they are still used pretty broadly.

We should go ahead and fix for pending since it's a core status, but I think we'll need to circle back to the discussion of adding some type of date_floating flag to fix this more broadly, or else break back compatibility by reverting to returning the actual stored database value for date_gmt instead of calculating it from date.

See: https://core.trac.wordpress.org/ticket/39953 for additional discussions and history on this one.