LibWeb: Implement the Screen interface

https://drafts.csswg.org/cssom-view/#the-screen-interface

Userland/Libraries/LibWeb/Forward.h

@@ -35,6 +35,7 @@ class CSSStyleRule;
 class CSSStyleSheet;
 class ElementInlineCSSStyleDeclaration;
 class Length;
+class Screen;
 class Selector;
 class StyleProperties;
 class StyleResolver;
@@ -297,6 +298,7 @@ class NodeWrapper;
 class PerformanceTimingWrapper;
 class PerformanceWrapper;
 class ProgressEventWrapper;
+class ScreenWrapper;
 class ScriptExecutionContext;
 class SubmitEventWrapper;
 class SVGElementWrapper;