fix: correctly match :has()'s selector during css pruning (#15277)

Fixes #14072

`:has()` was matching only against descendants or siblings, but not sibling's descendants. This makes the logic be able to go forward or backwards, simplifying a lot of cases along the way.

Author: 7nik

.changeset/cuddly-chefs-refuse.md

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+---
+'svelte': patch
+---
+
+fix: correctly match `:has()` selector during css pruning