updates theme.json to v2 for compatibility with filtering

[jacobdubail]

Description of the Change

This updates the theme.json version to v2 for compatibility with the new theme.json filters. It also updates keys to match v2 schema.

How to test the Change

Confirm custom styles are applying to the theme.

Changelog Entry

Changed - Updates theme.json to v2

Checklist:

• [ ] I agree to follow this project's Code of Conduct.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my change.
• [ ] All new and existing tests pass.

[fabiankaegy]

@jacobdubail If you want to you can also change the base of this PR to the trunk branch. We will want to use the update for the entire scaffold :)

[joesnellpdx]

@jacobdubail

We want to have the filter for the theme.json updates in here -right? Or is that still up for discussion?

[joesnellpdx]

ohh... @jacobdubail I see how you are doing it now.. and that's actually pretty slick!!