Register webfonts from theme.json

[aristath]

Description

This is a proof of concept for the discussion on #35591

To test:

• WordPress should have the patch from Webfonts API - webfonts collection implementation wordpress-develop#1736, implementing the webfonts API
• In a theme.json file add the following under settings.typography:

"webfonts": [
	{
		"fontFamily": "Source Serif Pro",
		"fontWeight": "200 900",
		"fontStyle": "normal",
		"fontStretch": "normal",
		"src": "file:./assets/fonts/source-serif-pro/SourceSerif4Variable-Roman.ttf.woff2",
		"provider": "local"
	},
	{
		"fontFamily": "Source Serif Pro",
		"fontWeight": "200 900",
		"fontStyle": "italic",
		"fontStretch": "normal",
		"src": "file:./assets/fonts/source-serif-pro/SourceSerif4Variable-Italic.ttf.woff2",
		"provider": "local"
	}
]

Easiest way to test is using the TT2 theme from https://github.com/aristath/twentytwentytwo

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 (please manually search all *.native.js files for terms that need renaming or removal).

[jorgefilipecosta]

I left a comment related to the API here #35591 (comment).

[jorgefilipecosta]

The logic seems to be the expected one and things seem to be on a good path. I have the opinion that we should not have a separate webfont key but instead nest things inside the fontFamilies. It is not a big change. In the future, we should look into providing this information to the editor so the editor knows which styles and weights are available for a font family. Without this connection, themes may select only some weights for a font in theme.json but users can still pick any so it seems like the weights are not used.