This is related to #17063 and is also a pre-request for the splash screen work.
This PR introduces 0 visual or functional changes. It just relocates the stylesheets in the load order.
`.css` stylesheets block the browser render. We need to move those out of the <head> tag.
However, they still need to be loaded before core/plugin/theme rendered HTML to avoid FOUC.
2f66eb59c2