Support CSS Variables in Popper offsets

[NicholasBoll]

🐛 Bug Report

The Popper offsets plugin doesn't support CSS variables. Integer pixel values are built into the core of Popper and the next floating UI iteration. It is possible to support CSS variables though, but we'd have to maintain our own offset plugin.

• Popper offset logic
• Popper style setting logic
• Example custom Popper modifier