feat(Avatar): use vanilla extract (#5467)

* fix: vanilla extract avatar

* fix: use css variables

* fix: tests

Author: lisalupi

.changeset/rotten-coins-glow.md

@@ -0,0 +1,5 @@
+---
+"@ultraviolet/ui": major
+---
+
+Refactor components `Avatar` to use vanilla-extract instead of Emotion