LibWeb/CSP: Implement the script-src directive

Author: https://github.com/Lubrsi
Commit: 0cff47828d
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/5328
Reviewed-by: https://github.com/ADKaster ✅

Libraries/LibWeb/Forward.h

@@ -138,6 +138,7 @@ class ImageSourceDirective;
 class ManifestSourceDirective;
 class MediaSourceDirective;
 class ObjectSourceDirective;
+class ScriptSourceDirective;
 struct SerializedDirective;
 
 }