[FIX] web_editor: error while changing background color of button

Before this commit:

When we want to change the background color of a button, clicking on that button
will occur traceback(dropdown is not a function).

After this commit:

Traceback will not occur by initializing the dropdown component as it has
converted into the OWL component.

Task-2916277

closes odoo/odoo#96508

Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>

addons/web_editor/static/src/js/wysiwyg/wysiwyg.js

@@ -1572,7 +1572,9 @@ const Wysiwyg = Widget.extend({
                             oldColorpicker.destroy();
                         }
                         manualOpening = true;
-                        $dropdown.children('.dropdown-toggle').dropdown('show');
+                        const $childElement = $dropdown.children('.dropdown-toggle');
+                        const dropdownToggle = new Dropdown($childElement);
+                        dropdownToggle.show();
                         const $colorpicker = $dropdown.find('.colorpicker');
                         const colorpickerHeight = $colorpicker.outerHeight();
                         const toolbarContainerTop = dom.closestScrollable(this.toolbar.el).getBoundingClientRect().top;