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/cssrule.rs

@@ -6,7 +6,7 @@ use std::cell::Cell;
 
 use dom_struct::dom_struct;
 use style::shared_lock::SharedRwLock;
-use style::stylesheets::CssRule as StyleCssRule;
+use style::stylesheets::{CssRule as StyleCssRule, CssRuleType};
 
 use crate::dom::bindings::codegen::Bindings::CSSRuleBinding::CSSRuleMethods;
 use crate::dom::bindings::inheritance::Castable;
@@ -147,7 +147,14 @@ impl CSSRule {
 impl CSSRuleMethods for CSSRule {
     // https://drafts.csswg.org/cssom/#dom-cssrule-type
     fn Type(&self) -> u16 {
-        self.as_specific().ty()
+        let rule_type = self.as_specific().ty() as u16;
+        // Per https://drafts.csswg.org/cssom/#dom-cssrule-type for constants > 15
+        // we return 0.
+        if rule_type > 15 {
+            0
+        } else {
+            rule_type
+        }
     }
 
     // https://drafts.csswg.org/cssom/#dom-cssrule-parentstylesheet
@@ -171,7 +178,7 @@ impl CSSRuleMethods for CSSRule {
 }
 
 pub trait SpecificCSSRule {
-    fn ty(&self) -> u16;
+    fn ty(&self) -> CssRuleType;
     fn get_css(&self) -> DOMString;
     /// Remove parentStylesheet from all transitive children
     fn deparent_children(&self) {