Expand field specification with new element for "all day"

WIP patch to add the necessary field schema changes.

This needs further work to update the internal APIs, and then fix existing data.

A test for the update script. Note that this kinda cheats because the field is not fully removed before the update script attempts to add it back again. Also, none of the internal APIs have been updated yet.

WIP, didn't want to loose it.

WIP to use hook_field_widget_form_alter() to add the all-day option.

Further WIP.

Further work.

I realized that now we have a specific value for indicating "this is an all-day thing" we don't need most of the code in theme_date_all_day().

The one code test works, now to fix the update script, clean up the code, write more tests, and look at backwards compatibility. Little things ;-)

I realized it was looking for the wrong field name - the suffix is "all_day" rather than "is_all_day". It also didn't need to fully clear the caches, just rebuild the schema.

Tests are green! Woot!
Next off:

• Update the new update script to verify the columns were actually removed during the prep work.
• Code cleanup.
• More test coverage.
• Regression testing, including testing other modules.
• Write a change notice.
• Update the issue summary.
• Anything else?

Spotted another bug - when you try to set a date to "all day" and it is using the "text field" widget it gives an error if the value includes a time portion, e.g. "07/22/2021 - 17:30" might be the default value from the widget but it fails, it actually requires the value "07/22/2021" in order to pass validation.

This includes the following changes:

• Test coverage for the "Text field" widget, that fails.
• Cleaned up date_all_day_field() to remove unused code.
• Updated date_field_all_day() to match date_all_day_field().

I know the first one will fail, hopefully the others are ok.

The field validation needed to be changed for the all_day validation to work. That one test works correctly, let's test the whole thing.

Refactoring the tests to rep for more test coverage.

New content type.

More test coverage.

So that fixes the text field widget.

Now to add test coverage for the timestamp field and its widgets.

Test coverage for the timestamp field.

Doh. Typoo.

Do we need more test coverage, especially unit test coverage, of the all-day functionality? Any thoughts?

FYI #3201878 will focus on updating existing data to the new system.

We need to identify whether other modules break because of the change. We also need to test it with e.g. timezone changes.

I also wonder if this should require a new branch, i.e. to take over the 7.x-3.x branch?

I created a draft change notice.

Will do new issues for some of the pieces.

I've committed this as-is to the 7.x-3.x branch.