Components: Fix Post Publishing Popover moving when certain dates are clicked

[allilevine]

Description

Fix Post Publishing popover glitch by changing the popover anchor ref to the containing div (PanelRow). Requires changing PanelRow to accept a forwarding ref.

Alternatively, we can change PanelRow to accept a ref as a prop and include the forwardRef() wrapper in PostSchedule instead.

Fixes #29899

How has this been tested?

• Add or edit a post.
• Open the Post Publishing popover by clicking on the publish date or "Immediately."
• Click on various dates in the picker and confirm that the popover does not move or change position.
• Regression: check that other instances of the PanelRow component function correctly and don't require a ref.

Screenshots

Types of changes

Bug fix:

• Changes the PanelRow component to accept a forwarding ref
• Creates a ref in PostSchedule and assigns it to PanelRow
• Passes the ref to Dropdown as an anchor ref and popover prop

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 (please manually search all *.native.js files for terms that need renaming or removal).

[retrofox]

LGTM. Although I guess it's possible to deal with this visual issue via CSS keeping the popover stuck to a position, this solution looks good to me.
I'd like to know the opinion of core folks, though.
@ellatrix @youknowriad could you chime on this, please?

[retrofox]

Thanks, Allison for dealing with this uncomfortably annoying visual issue 😅. Considering that the approach doesn't have any objection and it works well, I'm going to merge it.