Keep post publishing popover open when a date is clicked, by default

[allilevine]

Description

Follow-up to #29738 to remove the keepOpen prop and keep focus on the date picker by default.

How has this been tested?

1. Create a new post
2. Open the schedule popover by clicking on the publish date
3. Click on a date in the picker and confirm that the popover does not close.
4. Navigate to the next month
5. Click on a date and confirm that the popover does not close.
6. Navigate to a date via the keyboard and select it. Confirm that the popover does not close.

Screenshots

Gif of the popover staying open after clicking on a date:

Types of changes

Bug fix: Uses keepFocusInside() to keep the date picker open on date change.

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR.

[retrofox]

LGTM.

Thanks, Allison. Tested in the editor as well as in the storybook. 👍

[youknowriad]

Thanks for the follow-up :)