Post Featured Image Block: Border radius and color not applied on overlay

[RahiDroid]

What?

• Fixes border-radius not being applied to the overlay when added from the theme.json file.
• Fixes border-radius not being applied to the overlay when different values are added for each corner/side.
• Fixes border-color not being applied on the overlay.

Why?

• Partially covers Border radius is not applied to overlay element #44262

How?

• Uses the style engine-generated attributes for the border and passes it on to the Overlay element.

Testing instructions

Screenshots or screencast

Before	After

[mikachan]

Thanks for this! It's working well for me, and I like the way you've used get_block_core_post_featured_image_border_attributes for the border styles.

[aaronrobertshaw]

Thanks for working on this @RahiDroid 👍

As noted in my comment on #44262, we've got some overlap between our PRs addressing these overlay issues.

#44286 also addresses a problem where the markup relating to the overlay is rendered in the editor when it isn't on the frontend.

If it is ok with you, I'd like to close this PR in favour of #44286. What do you think?

[aaronrobertshaw]

As discussed, closing this one in favour of #44286

Note: I see this had another commit pushed after ok to close it however it missed adding the border classes to the overlay in the editor as the other PR does. So we'll still proceed with #44286