Add Box Shadow support for featured image

[bph]

What problem does this address?

In templates, features image are a major design element for Archive pages, and it would be expanded the design tools considerably if the box shadow support that is now available for the image block could also be provided for the featured image block.

What is your proposed solution?

Open up box shadow support to featured image (among other blocks)

[colinduwe]

@bph I submitted a PR for this. Please have a look.

[bph]

@colinduwe Did you get a chance to go over @aaronrobertshaw comments on the PR?

[colinduwe]

@bph and @aaronrobertshaw I did look at the comments which led me down the path of trying to make a PR just for the https://github.com/WordPress/gutenberg/blob/trunk/lib/block-supports/shadow.php file so if a block adds __experimentalSkipSerialization the styles are not output on the block wrapper element. But then I started testing with the core/column block and adding __experimentalSkipSerialization works as expected without the PR. I'm still trying to understand what's different between core/column and core/post-featured-image.

[aaronrobertshaw]

I'm still trying to understand what's different between core/column and core/post-featured-image.

The difference you encountered is that the core/column block is a static block while the core/post-featured-image block is dynamic.

The issue with skipping serialization is specific to dynamic blocks and is why it is limited to the PHP hook that applies the shadow support.