LibWeb: Implement CanvasRenderingContext2D.save()

Author: https://github.com/linusg
Commit: 7d435b5ada
Pull-request: https://github.com/SerenityOS/serenity/pull/11444

Userland/Libraries/LibWeb/HTML/CanvasRenderingContext2D.idl

@@ -31,6 +31,8 @@ interface CanvasRenderingContext2D {
     ImageData createImageData(double sw, double sh);
     undefined putImageData(ImageData imagedata, double dx, double dy);
 
+    undefined save();
+
     readonly attribute HTMLCanvasElement canvas;
 
 };