Snippets: Make it easier for plugins to add snippets groups

Groups are no longer enum values but identified from snippet providers.

src/plugins/qmljseditor/qmljseditorconstants.h

@@ -60,6 +60,7 @@ const char *const TASK_CATEGORY_QML = "Task.Category.Qml";
 const char * const WIZARD_CATEGORY_QML = "S.Qml";
 const char * const WIZARD_TR_CATEGORY_QML = QT_TRANSLATE_NOOP("QmlJsEditor", "QML");
 
+const char * const QML_SNIPPETS_GROUP_ID = "QML";
 
 } // namespace Constants
 } // namespace QmlJSEditor