Editor: Add block theme infrastructure

Adds the required infrastructure to render block-based themes. This is sourced
from the Gutenberg plugin.

Fixes #54335.
Props bernhard-reiter, youknowriad, ntsekouras, hellofromtonya.


git-svn-id: https://develop.svn.wordpress.org/trunk@52062 602fd350-edb4-49c9-b593-d223f7449a82

tools/webpack/blocks.js

@@ -53,6 +53,7 @@ module.exports = function( env = { environment: 'production', watch: false, buil
 		'site-title',
 		'social-link',
 		'tag-cloud',
+		'template-part',
 	];
 	const blockFolders = [
 		'audio',