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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components/script/dom/cssgroupingrule.rs

@@ -8,7 +8,6 @@ use style::shared_lock::{Locked, SharedRwLock};
 use style::stylesheets::{CssRuleTypes, CssRules as StyleCssRules};
 
 use crate::dom::bindings::codegen::Bindings::CSSGroupingRuleBinding::CSSGroupingRuleMethods;
-use crate::dom::bindings::codegen::Bindings::CSSRuleBinding::CSSRule_Binding::CSSRuleMethods;
 use crate::dom::bindings::error::{ErrorResult, Fallible};
 use crate::dom::bindings::inheritance::Castable;
 use crate::dom::bindings::reflector::DomObject;
@@ -69,7 +68,8 @@ impl CSSGroupingRuleMethods for CSSGroupingRule {
     // https://drafts.csswg.org/cssom/#dom-cssgroupingrule-insertrule
     fn InsertRule(&self, rule: DOMString, index: u32) -> Fallible<u32> {
         // TODO: this should accumulate the rule types of all ancestors.
-        let containing_rule_types = CssRuleTypes::from_bits(self.cssrule.Type().into());
+        let rule_type = self.cssrule.as_specific().ty();
+        let containing_rule_types = CssRuleTypes::from(rule_type);
         self.rulelist()
             .insert_rule(&rule, index, containing_rule_types)
     }