IDLGenerators: Set Iterator @@toStringTag with correct descriptor

Author: https://github.com/tcl3
Commit: b6ec055bf9
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3226

Tests/LibWeb/Text/expected/URL/url-search-params-iterator-iterator.txt

@@ -1,5 +1,5 @@
-[object Iterator]
-[object Iterator]
+[object URLSearchParams Iterator]
+[object URLSearchParams Iterator]
 true
 hello
 1

Tests/LibWeb/Text/expected/wpt-import/webidl/ecmascript-binding/default-iterator-object.txt

@@ -0,0 +1,8 @@
+Harness status: OK
+
+Found 3 tests
+
+3 Pass
+Pass	Default iterator objects for an interface have the same prototype
+Pass	Object.prototype.toString returns correct value
+Pass	@@toStringTag has correct value from prototype