Block Editor: port custom-spacing theme support

[nosolosw]

The property custom-spacing was deemed stable so it's ready to be ported to WordPress core during the 5.7 cycle, when trunk is open.

[noisysocks]

Hi @nosolosw. Are you able to add a patch for this? Not sure which PHP code needs to be copied over 🙂

[prbot]

​nosolosw commented on ​PR #951:

I've also prepared the changes in Gutenberg.

[nosolosw]

:wave: @noisysocks this needs two things:

• PR for wordpress-develop at ​https://github.com/WordPress/wordpress-develop/pull/951
• PR for Gutenberg 9.9 at ​https://github.com/WordPress/gutenberg/pull/28548

[gziolo]

This is ready to go with the patch included. I can commit it tomorrow unless @noisysocks beats me to it  😃

[noisysocks]

In 50070:

Block Editor: Add enableCustomSpacing

Adds the enableCustomSpacing editor setting. This enables the custom block
spacing feature from Gutenberg.

Props nosolosw, gziolo.
Fixes #51760.

[noisysocks]

Done. I think GB28548 needs some work though as that wasn't working for me when I tested it.

[nosolosw]

I pushed a fix and ​https://github.com/WordPress/gutenberg/pull/28548 is working fine now. Will be part of Gutenberg 9.9RC.

[TimothyBlynJacobs]

Ideally, we should be registering these in create_initial_theme_features.

[a4jp.com]

Thank you so much for doing this and if it's okay can you also make

div.block-editor-block-list__insertion-point.is-vertical

clickable and add the missing plus when you mouse over the top of the first block? It's missing now so impossible to add blocks before the first block. Thank you so much for making the accessibility option in WordPress heaps better with every update.