LibHTML: Support rendering <img src> with file:// URLs

We can now show images loaded from local file:// URLs. Pretty neat :^)

Libraries/LibHTML/DOM/HTMLImageElement.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <LibDraw/GraphicsBitmap.h>
 #include <LibHTML/DOM/HTMLElement.h>
 
 class HTMLImageElement : public HTMLElement {
@@ -10,6 +11,10 @@ public:
     String alt() const { return attribute("alt"); }
     String src() const { return attribute("src"); }
 
+    const GraphicsBitmap* bitmap() const;
+
 private:
     virtual RefPtr<LayoutNode> create_layout_node(const StyleResolver&, const StyleProperties* parent_style) const override;
+
+    mutable RefPtr<GraphicsBitmap> m_bitmap;
 };