Add block gap to Post Content block.

[tellthemachines]

What?

Partially addresses #48902. (I'm not sure how useful adding margin and padding to Post Content might be, though happy to also do so if it's desirable)

We should be able to set a custom spacing in Post Content.

Testing Instructions

Check that block gap can be set on Post Content at the block level as well as in global styles. Gap value should also be correctly reflected in the post editor.

[github-actions]

Flaky tests detected in 88d932d.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/6118324985
📝 Reported issues:

• [Flaky Test] should partially select with shift + click (@webkit) #53524 in /test/e2e/specs/editor/various/multi-block-selection.spec.js

[ramonjd]

This is working very well for me so far. Tested in 2023, 2022 and empty theme on post and page templates. Pages in the site editor appear as they do in the post editor as well.

I tried in various templates and blocks.

Before	After

__

[andrewserong]

This is testing very nicely for me, too. Great that all the prep work done separately means that this feature just works out of the box once it's switched on!

✅ Styles set in global styles are output correctly.
✅ Block-level block spacing within a template correctly overrides styles set in global styles.
✅ Styles are output correctly in post and page editor, and in the site editor, and editing a single page within the site editor.
✅ Block spacing (correctly) only applies to root level blocks within a post content block, and any nested blocks use their own block spacing values as expected.

Examining the styles in dev tools shows the styles are all being overridden correctly:

• User agent styles are overridden by the layout type's default spacing
• Layout type's default spacing is overridden by post content block in global styles
• Global styles spacing is overridden by block-level styles within the particular template

LGTM! ✨

[tellthemachines]

Thanks for reviewing and testing folks!