Auto merge of #23029 - KwanEsq:insertRuleNoIndex, r=SimonSapin

Update StyleSheet.insertRule WebIDL to make index optional.

Update wpt metadata to show the new passes.
Add one test as crashing since currently passing an \@import rule to insertRule
leads to "Expected a stylesheet loader for \@import"

---

- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #23025
- [x] There are tests for these changes
- [x] ./mach test-wpt css/cssom passes with these changes

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components/script/dom/webidls/CSSStyleSheet.webidl

@@ -7,6 +7,6 @@
 interface CSSStyleSheet : StyleSheet {
   // readonly attribute CSSRule? ownerRule;
   [Throws, SameObject] readonly attribute CSSRuleList cssRules;
-  [Throws] unsigned long insertRule(DOMString rule, unsigned long index);
+  [Throws] unsigned long insertRule(DOMString rule, optional unsigned long index = 0);
   [Throws] void deleteRule(unsigned long index);
 };

tests/wpt/metadata/css/cssom/insertRule-charset-no-index.html.ini

@@ -1,10 +0,0 @@
-[insertRule-charset-no-index.html]
-  [inserRule with charset and omitted index argument]
-    expected: FAIL
-
-  [insertRule with charset and undefined index argument]
-    expected: FAIL
-
-  [insertRule with charset and omitted index argument]
-    expected: FAIL
-

tests/wpt/metadata/css/cssom/insertRule-import-no-index.html.ini

@@ -1,7 +0,0 @@
-[insertRule-import-no-index.html]
-  [inserRule with import and omitted index argument]
-    expected: FAIL
-
-  [insertRule with import and omitted index argument]
-    expected: FAIL
-

tests/wpt/metadata/css/cssom/insertRule-namespace-no-index.html.ini

@@ -1,13 +1,3 @@
 [insertRule-namespace-no-index.html]
-  [inserRule with namespace and omitted index argument]
+  expected: CRASH
-    expected: FAIL
-
-  [inserRule with namespace and omitted index argument should insert import]
-    expected: FAIL
-
-  [insertRule with namespace and omitted index argument]
-    expected: FAIL
-
-  [insertRule with namespace and omitted index argument should insert import]
-    expected: FAIL
 

tests/wpt/metadata/css/cssom/insertRule-no-index.html.ini

@@ -1,10 +0,0 @@
-[insertRule-no-index.html]
-  [inserRule with omitted index argument]
-    expected: FAIL
-
-  [insertRule with undefined index argument]
-    expected: FAIL
-
-  [insertRule with omitted index argument]
-    expected: FAIL
-

tests/wpt/metadata/css/cssom/interfaces.html.ini

@@ -243,9 +243,6 @@
   [MediaList interface: calling deleteMedium(CSSOMString) on style_element.sheet.media with too few arguments must throw TypeError]
     expected: FAIL
 
-  [CSSStyleSheet interface: operation insertRule(CSSOMString, unsigned long)]
-    expected: FAIL
-
   [CSSStyleSheet interface: style_element.sheet must inherit property "ownerRule" with the proper type]
     expected: FAIL