LibWeb: Replace IDL 'void' return type with 'undefined'

From the Web IDL spec: https://heycam.github.io/webidl/#idl-undefined

[...]
undefined constant values in IDL are represented with the `undefined`
token.
[...]
Note: This value was previously spelled `void`, and more limited in how
it was allowed to be used.

Libraries/LibWeb/CodeGenerators/WrapperGenerator.cpp

@@ -741,7 +741,7 @@ static @fully_qualified_name@* impl_from(JS::VM& vm, JS::GlobalObject& global_ob
         auto scoped_generator = generator.fork();
         scoped_generator.set("return_type", return_type.name);
 
-        if (return_type.name == "void") {
+        if (return_type.name == "undefined") {
             scoped_generator.append(R"~~~(
     return JS::js_undefined();
 )~~~");
@@ -918,7 +918,7 @@ JS_DEFINE_NATIVE_FUNCTION(@wrapper_class@::@function.name:snakecase@)
 
         function_generator.set(".arguments", arguments_builder.string_view());
 
-        if (function.return_type.name != "void") {
+        if (function.return_type.name != "undefined") {
             function_generator.append(R"~~~(
     auto retval = impl->@function.name:snakecase@(@.arguments@);
 )~~~");

Libraries/LibWeb/DOM/Element.idl

@@ -3,7 +3,7 @@ interface Element : Node {
     readonly attribute DOMString tagName;
 
     DOMString? getAttribute(DOMString qualifiedName);
-    void setAttribute(DOMString qualifiedName, DOMString value);
+    undefined setAttribute(DOMString qualifiedName, DOMString value);
 
     readonly attribute Element? firstElementChild;
     readonly attribute Element? lastElementChild;

Libraries/LibWeb/DOM/Event.idl

@@ -7,14 +7,14 @@ interface Event {
 
     readonly attribute unsigned short eventPhase;
 
-    void stopPropagation();
+    undefined stopPropagation();
     attribute boolean cancelBubble;
-    void stopImmediatePropagation();
+    undefined stopImmediatePropagation();
 
     readonly attribute boolean bubbles;
     readonly attribute boolean cancelable;
     attribute boolean returnValue;
-    void preventDefault();
+    undefined preventDefault();
     readonly attribute boolean defaultPrevented;
     readonly attribute boolean composed;
 

Libraries/LibWeb/DOM/EventTarget.idl

@@ -1,6 +1,6 @@
 interface EventTarget {
 
-    void addEventListener(DOMString type, EventListener? callback);
-    void removeEventListener(DOMString type, EventListener? callback);
+    undefined addEventListener(DOMString type, EventListener? callback);
+    undefined removeEventListener(DOMString type, EventListener? callback);
 
 };

Libraries/LibWeb/HTML/CanvasRenderingContext2D.idl

@@ -1,28 +1,28 @@
 interface CanvasRenderingContext2D {
 
-    void fillRect(double x, double y, double w, double h);
-    void strokeRect(double x, double y, double w, double h);
+    undefined fillRect(double x, double y, double w, double h);
+    undefined strokeRect(double x, double y, double w, double h);
 
-    void scale(double x, double y);
-    void translate(double x, double y);
-    void rotate(double radians);
+    undefined scale(double x, double y);
+    undefined translate(double x, double y);
+    undefined rotate(double radians);
 
-    void beginPath();
-    void closePath();
-    void fill(DOMString fillRule);
-    void stroke();
-    void moveTo(double x, double y);
-    void lineTo(double x, double y);
-    void quadraticCurveTo(double cpx, double cpy, double x, double y);
+    undefined beginPath();
+    undefined closePath();
+    undefined fill(DOMString fillRule);
+    undefined stroke();
+    undefined moveTo(double x, double y);
+    undefined lineTo(double x, double y);
+    undefined quadraticCurveTo(double cpx, double cpy, double x, double y);
 
-    void drawImage(HTMLImageElement image, double dx, double dy);
+    undefined drawImage(HTMLImageElement image, double dx, double dy);
 
     attribute DOMString fillStyle;
     attribute DOMString strokeStyle;
     attribute double lineWidth;
 
     ImageData createImageData(double sw, double sh);
-    void putImageData(ImageData imagedata, double dx, double dy);
+    undefined putImageData(ImageData imagedata, double dx, double dy);
 
     readonly attribute HTMLCanvasElement canvas;
 

Libraries/LibWeb/HTML/HTMLFormElement.idl

@@ -5,6 +5,6 @@ interface HTMLFormElement : HTMLElement {
     [Reflect=accept-charset] attribute DOMString acceptCharset;
     [Reflect=novalidate] attribute boolean noValidate;
 
-    void submit();
+    undefined submit();
 
 };