LibDraw: Rename ImageLoader => ImageDecoder

ImageLoader was not the right name for this, as there is no loading
happening, only decoding. :^)

Libraries/LibDraw/ImageDecoder.h

@@ -0,0 +1,35 @@
+#pragma once
+
+#include <AK/NonnullRefPtr.h>
+#include <AK/OwnPtr.h>
+#include <AK/RefCounted.h>
+#include <LibDraw/Size.h>
+
+class GraphicsBitmap;
+
+class ImageDecoderPlugin {
+public:
+    virtual ~ImageDecoderPlugin() {}
+
+    virtual Size size() = 0;
+    virtual RefPtr<GraphicsBitmap> bitmap() = 0;
+
+protected:
+    ImageDecoderPlugin() {}
+};
+
+class ImageDecoder : public RefCounted<ImageDecoder> {
+public:
+    static NonnullRefPtr<ImageDecoder> create(const u8* data, size_t size) { return adopt(*new ImageDecoder(data, size)); }
+    ~ImageDecoder();
+
+    Size size() const { return m_plugin->size(); }
+    int width() const { return size().width(); }
+    int height() const { return size().height(); }
+    RefPtr<GraphicsBitmap> bitmap() const { return m_plugin->bitmap(); }
+
+private:
+    ImageDecoder(const u8*, size_t);
+
+    mutable OwnPtr<ImageDecoderPlugin> m_plugin;
+};