Blockbase: Use the Global Styles rest API in the customizer

[scruffian]

In WordPress/gutenberg#35801 a Global Styles API was introduced. We should reconsider the implementation of our Customizer/Global Styles bridge, to take advantage of this new API.

Alternatively we could just use the new style switcher in Gutenberg.

From #5307

[MaggieCabrera]

I agree. Skatepark could have different variations with and without duotone and avoid the customizer route altogether