Reduce the amount of data Global Styles sends to the client

[oandregal]

The different block editors receive data from the server via settings in the form of wp.editSite.initialize( 'edit-site-editor', settings ). This can be seen either embedded in the HTML head or directly in the corresponding store, for example, core/site-editor.

There are a couple of issues with how global-styles.php currently sends the data to the client.

• There are some data that we may be able to calculate in the client, because it's extracted from block.json data. This is for __experimentalGlobalStylesContexts.

• The more pressing is that we send empty data in both __experimentalFeatures and __experimentalGlobalStylesBaseStyles for each registered block, which amounts to a very noticeable number of unnecesary bits send over the wire. The reason for that is how we normalize the schema for every context. Fixed in Extract theme json processor  #26803

[oandregal]

I'm working on a reorganization that changes how we normalize/validate the schema and will address the second issue.