[IMP] website: keep the selected image after moving it in gallery

Keep the selected image after moving it in the gallery. So that the
options for moving the current image are always displayed.

Part of https://github.com/odoo/odoo/pull/45096
task-2162952

addons/website/static/src/snippets/s_image_gallery/options.js

@@ -212,6 +212,7 @@ options.registry.gallery = options.Class.extend({
             .addClass('o_' + widgetValue);
         this[widgetValue]();
         this.trigger_up('cover_update');
+        this._refreshPublicWidgets();
     },
     /**
      * Displays the images with the standard layout: floating images.
@@ -316,13 +317,32 @@ options.registry.gallery = options.Class.extend({
                     imgs.push(data.$image[0]);
                     break;
             }
+            position = imgs.indexOf(data.$image[0]);
             _.each(imgs, function (img, index) {
                 // Note: there might be more efficient ways to do that but it is
                 // more simple this way and allows compatibility with 10.0 where
                 // indexes were not the same as positions.
                 $(img).attr('data-index', index);
             });
-            this.mode('reset', this.getMode());
+            const currentMode = this.getMode();
+            this.mode('reset', currentMode);
+            if (currentMode === 'slideshow') {
+                const $carousel = this.$target.find('.carousel');
+                $carousel.removeClass('slide');
+                $carousel.carousel(position);
+                this.$target.find('.carousel-indicators li').removeClass('active');
+                this.$target.find('.carousel-indicators li[data-slide-to="' + position + '"]').addClass('active');
+                this.trigger_up('activate_snippet', {
+                    $snippet: this.$target.find('.carousel-item.active img'),
+                    ifInactiveOptions: true,
+                });
+                $carousel.addClass('slide');
+            } else {
+                this.trigger_up('activate_snippet', {
+                    $snippet: data.$image,
+                    ifInactiveOptions: true,
+                });
+            }
         }
     },