Move _isShown() method to private section (#41220)

js/src/collapse.js

@@ -204,11 +204,11 @@ class Collapse extends BaseComponent {
     this._queueCallback(complete, this._element, true)
   }
 
+  // Private
   _isShown(element = this._element) {
     return element.classList.contains(CLASS_NAME_SHOW)
   }
 
-  // Private
   _configAfterMerge(config) {
     config.toggle = Boolean(config.toggle) // Coerce string values
     config.parent = getElement(config.parent)