Add the ability to export color or typography only style variations

[annezazu]

To stay up to date on new options coming to 6.6, wanted to flag the new ability to surface color and typography only variations: WordPress/gutenberg#61215 Adding the option to export a color or typography only variation explicitly would go a long way for adoption and save theme devs a lot of time.

Shout out to @richtabor for raising this.