Improved variant ordering

[ben-rogerson]

This PR fixes the ordering of variants on multi-variant classes:

tw`hover:[svg]:block`

// ↓ ↓ ↓ ↓ ↓ ↓

// Before
({ "svg:hover": { "display": "block" } });

// Now
({ ":hover svg": { "display": "block" } });

Thanks @u3u for the report which led me to look into this issue again - turned out an easy fix this time 🎉

The auto-parent selector then needed a couple tweaks:

• Removed an error that asked us to add parent selectors
• Included elements as a qualifier for a & (amp+space) prefix

I also fixed an error when non-media at-rules were used in arbitrary variants. (eg: [@page]:m-0)