[Editor] Add a basic stamp editor (bug 1790255)

For now it allows to add a stamp annotation with an image selected from the file system.

src/display/annotation_layer.js

@@ -3011,4 +3011,9 @@ class AnnotationLayer {
   }
 }
 
-export { AnnotationLayer, FreeTextAnnotationElement, InkAnnotationElement };
+export {
+  AnnotationLayer,
+  FreeTextAnnotationElement,
+  InkAnnotationElement,
+  StampAnnotationElement,
+};