Block Library: Add 'object-position' to allowed inline style attributes list

[Mamaduka]

Description

The object-position property, used by the Cover block, isn't in the list of allowed CSS attributes. It's removed from the content when non-admin users save a post.

Fixes #29907.

How has this been tested?

1. Create a post with a cover block.
2. Edit it as an Author user.
3. Update cover block's focal point.
4. Save and refresh the page.
5. Editor shouldn't display the cover block in recovery mode.

Types of changes

Bugfix

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.

[Mamaduka]

Core trac ticket: https://core.trac.wordpress.org/ticket/52961.

[aristath]

LGTM 👍

Note: When this gets merged backported to core, object-position should simply be added in the array of allowed attributes inside the safecss_filter_attr function instead.

[Mamaduka]

Thanks, @aristath, for the review.

Note: When this gets merged backported to core, object-position should simply be added in the array of allowed attributes inside the safecss_filter_attr function instead.

Right, I also create PR for it WordPress/wordpress-develop#1156.

My question is if we should keep fallback in the plugin while supporting a non backported core version.

[aristath]

Right, I also create PR for it WordPress/wordpress-develop#1156.

Awesome 👍

My question is if we should keep fallback in the plugin while supporting a non backported core version.

I'd say yes. The Gutenberg plugin needs to support previous versions of WP and not just the latest one, so this will need to be there.
I would suggest adding a comment in the function stating that it should be removed when the minimum required version is >= 5.8.
We could also add a check and instead of $attrs[] = 'object-position'; do

if ( ! in_array( 'object-option', $attrs ) ) {
    $attrs[] = 'object-position';
}

or instead of return $attrs; do return array_unique( $attrs );, but that may be a bit overkill, there's no real harm in having a duplicate value in that array

[Mamaduka]

there's no real harm in having a duplicate value in that array

Agree. Added note about removal.

I'll merge this if it's okay with you.

[aristath]

Agree. Added note about removal.

Thank you :)

I'll merge this if it's okay with you.

Agreed

[Mamaduka]

Changes are merged into the core. Changeset https://core.trac.wordpress.org/changeset/50649