Global Styles: Add a way to set defaults for all styles

[scruffian]

If I declare support for a global style in a block I'd also like to be able to set a default value for that block. For example I could set default values for padding in the block attributes like this:

		"spacing": {
			"type": "object",
			"default": {
				"padding": {
					"type": "number",
					"default": 10
				}
			}
		},

I think this is already supported by some properties but either this one doesn't work, or I'm doing it wrong!

[scruffian]

This is achievable now, the syntax is like this:

"style": { "default": { "spacing": { "padding": { "default": 10 } } } }

It might be good to document this

[scruffian]

There also seem to be two bugs with this:

1. If you set a default value it's not reflected in the block - is it expected that this is set in CSS?
2. If you reset the control it wipes the value rather than going back to the default.

[oandregal]

I think I may benefit from some more context on the specifics you're working with! Is this something you do with theme.json (presumably not because I don't know how you'd do it), or are you working with a block and so trying to create its block.json (block supports docs, in case they're helpful)? If it is the latter, you can add defaults (there's an example about padding in the docs).

[scruffian]

Ah yes, that's what I'm doing. Sorry I hadn't seen the docs. I think the bugs I mentioned above are still relevant though.

[oandregal]

@scruffian I found #27341 which I believe is what prompted you to file this issue?

I left a few comments there, but, essentially instead of default you need to use top, right, bottom, left ― see the documentation for padding. As per the control, I believe it works as designed (remove any style value).

[gziolo]

Would be it fine to define this default value inside supports rather than passing true? It’d more convenient for developers.

[scruffian]

Closing in favour of #27796