LibWeb: Expose barebones CSSStyleDeclaration to JavaScript

You can now access an element's inline style via Element.style.
The interface is not very capable yet though. :^)

Userland/Libraries/LibWeb/DOM/Element.h

@@ -92,6 +92,8 @@ public:
 
     const CSS::CSSStyleDeclaration* inline_style() const { return m_inline_style; }
 
+    NonnullRefPtr<CSS::CSSStyleDeclaration> style_for_bindings();
+
     // FIXME: innerHTML also appears on shadow roots. https://w3c.github.io/DOM-Parsing/#dom-innerhtml
     String inner_html() const;
     void set_inner_html(StringView);