Fix InsertRule to use the right CssRuleTypes (#32125)

`CSSRule::Type()` returns an u16 for CSSOM. `InsertRule()` was
incorrectly using this to create a `CssRuleTypes`.

Instead of `CssRuleTypes::from_bits(rule_type)`, it should be something
like `CssRuleTypes::from_bits(1 << rule_type)`.

However, that would only work when `Type()` provides an actual value,
which per https://drafts.csswg.org/cssom/#dom-cssrule-type only happens
for old rule types. New rule types just return 0.

Therefore, this patch changes the signature of `SpecificCSSRule::ty()`
to return the actual `CssRuleType`, and then `CSSRule::Type()` can zero
it out when necessary.

The fix is only relevant for CSS Nesting, which is currently disabled on
Servo, so no test is necessary.

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relevant for CSS Nesting, which is currently disabled

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components/script/dom/cssmediarule.rs

@@ -5,7 +5,7 @@
 use dom_struct::dom_struct;
 use servo_arc::Arc;
 use style::shared_lock::ToCssWithGuard;
-use style::stylesheets::MediaRule;
+use style::stylesheets::{CssRuleType, MediaRule};
 use style_traits::ToCss;
 
 use crate::dom::bindings::codegen::Bindings::CSSMediaRuleBinding::CSSMediaRuleMethods;
@@ -68,9 +68,8 @@ impl CSSMediaRule {
 }
 
 impl SpecificCSSRule for CSSMediaRule {
-    fn ty(&self) -> u16 {
-        use crate::dom::bindings::codegen::Bindings::CSSRuleBinding::CSSRuleConstants;
-        CSSRuleConstants::MEDIA_RULE
+    fn ty(&self) -> CssRuleType {
+        CssRuleType::Media
     }
 
     fn get_css(&self) -> DOMString {