Starting to set up global styles and refactor existing background components

Porting over existing hook code to shared, global styles component.
Next step is to gut the existing hook and set up props using setAttribute etc

…ing with blocks. I think that's the way it works.

We don't need useSettingsForBlockElement() yet because we're not dealing with blocks. I think that's the way it works.

…Size value for block backgrounds is 'cover'

… cover

We don't use named values yet, only percentages, so it should be safe

…e is "indirectly" stored in an array, at least determined by multiple values in an array.

Co-authored-by: Andrew Serong <14988353+andrewserong@users.noreply.github.com>