Auto merge of #19195 - wilsoniya:issue-16840, r=emilio

style: :dir() pseudo class now represented by enum

`:dir()` pseudo class param now represented as enum variants.

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #16840
- [X] There are tests for these changes

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components/selectors/gecko_like_types.rs

@@ -10,6 +10,7 @@
 pub enum PseudoClass {
     Bare,
     String(Box<[u16]>),
+    Dir(Box<()>),
     MozAny(Box<[()]>),
 }