LibWeb: Add input stepUp and stepDown functions

Author: https://github.com/bplaat
Commit: 1b9a961fb0
Pull-request: https://github.com/SerenityOS/serenity/pull/22166
Reviewed-by: https://github.com/LucasChollet
Reviewed-by: https://github.com/shannonbooth
Reviewed-by: https://github.com/trflynn89 ✅

Userland/Libraries/LibWeb/HTML/HTMLInputElement.idl

@@ -44,8 +44,8 @@ interface HTMLInputElement : HTMLElement {
     attribute unrestricted double valueAsNumber;
     // FIXME: [CEReactions] attribute unsigned long width;
 
-    // FIXME: undefined stepUp(optional long n = 1);
-    // FIXME: undefined stepDown(optional long n = 1);
+    undefined stepUp(optional long n = 1);
+    undefined stepDown(optional long n = 1);
 
     // FIXME: readonly attribute boolean willValidate;
     // FIXME: readonly attribute ValidityState validity;