Enhance create block theme UI [experimental]
This change aims at improving UI of the create block theme by moving to react components. Also keeps the UI consistent with font management.
Old:
Following is the new work in progress UI.

@beafialho @henriqueiamarino could you please share your thoughts and feedback on this. I am not sure if it is still right to keep the generate button on the left.
Note: This is UI only change for now to gain early feedback, and complete functionality is not ported yet.
Related WIP issues:
https://github.com/WordPress/create-block-theme/issues/322 https://github.com/WordPress/create-block-theme/pull/294
What do you think about moving all of this to the Site Editor plugin screen?
I think it would be really nice to not have to leave the site editor to add the fonts.
Closing this as all theme export options are now moved to site editor.