When republishing a news item, the previous display time gets replaced with today's date

When a news item is published, it gets a Publication Time (which is usually displayed to the public). Sometimes the item needs to be edited, say to correct a typo, but the publication date should not change. In the Publish screen an author can set a Display Time, which will then be used as the Publication Time in a rendered news item. If a news item is edited again, it should retain the Display Time. However in 3.x the current datetime gets inserted in the Display Time field. The Author would have to manually re-enter the old Display Time in order to preserve it. The field should be sticky and contain the Display Time set on the previous version.

This bug relates directly to #1155697