fix: image horizontal flip fix + improved tests (#5799)

Co-authored-by: Antonio Della Fortuna <a.dellafortuna00@gmail.com>
Co-authored-by: dwelle <luzar.david@gmail.com>
fixes https://github.com/excalidraw/excalidraw/issues/5784

src/element/resizeElements.ts

@@ -557,10 +557,10 @@ export const resizeSingleElement = (
     mutateElement(element, {
       scale: [
         // defaulting because scaleX/Y can be 0/-0
-        (Math.sign(scaleX) || stateAtResizeStart.scale[0]) *
-          stateAtResizeStart.scale[0],
-        (Math.sign(scaleY) || stateAtResizeStart.scale[1]) *
-          stateAtResizeStart.scale[1],
+        (Math.sign(newBoundsX2 - stateAtResizeStart.x) ||
+          stateAtResizeStart.scale[0]) * stateAtResizeStart.scale[0],
+        (Math.sign(newBoundsY2 - stateAtResizeStart.y) ||
+          stateAtResizeStart.scale[1]) * stateAtResizeStart.scale[1],
       ],
     });
   }