Lesson update - Style variations

Update style variations to include color and typography only options

https://github.com/WordPress/Learn/issues/2194#issuecomment-2155422371 Pulling this out of the prior lesson on style variations. Color and Typography only style variation options will be available for block themer authors to create for 6.6: https://github.com/WordPress/gutenberg/issues/61215

To pull from the 6.6 source of truth:

Theme style variations allow you to change the look and feel of your site, all while using the same theme. To build on the design possibilities of a block theme with style variations, 6.6 adds the ability to target color or typography only variations and offers them as presets, separate from overall style variations. Whereas style variations can change virtually anything, these new color and typography presets offer more contained changes, making it simple to offer broader color options or typography options out of the box. Theme authors will need to target this new option specifically by creating color or typography only variations without creating wholesale new style variations. For any style variations that only contain color and typography only changes, these will now automatically appear in this separate preset flow.

cc @jonathanbossenger

Review the lesson discussed in the linked Learn issue comment and compare it with the WordPress 6.6 style-variation guidance in the linked Gutenberg issue. Update the lesson to cover color-only and typography-only variations, and confirm that the explanation distinguishes these presets from full style variations.