Add resizing options "long edge" and "short edge" (#6263)

Introduces "long edge" and "short edge" options to resize an image. The GUI is made such that the relevant spinboxes only appear for the selected option. Unrelated values (e.g. for box-mode) are not updated.

rtengine/procparams.h

@@ -1690,6 +1690,8 @@ struct ResizeParams {
     int dataspec;
     int width;
     int height;
+    int longedge;
+    int shortedge;
     bool allowUpscaling;
 
     ResizeParams();