Doc: Fix QDoc warnings issued for Core plugin ActionManager docs

Fix warnings for:

- ActionContainer
- ActionManager
- Command
- CommandButton
- CommandMappings
- CommandsFile

Task-number: QTCREATORBUG-23584
Change-Id: I3c7903e054d43143885d67d64309d1ae4429de2c
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/coreplugin/actionmanager/commandmappings.cpp

@@ -123,6 +123,12 @@ public:
 
 } // namespace Internal
 
+/*!
+    \class Core::CommandMappings
+    \inmodule QtCreator
+    \internal
+*/
+
 CommandMappings::CommandMappings(QWidget *parent)
     : QWidget(parent), d(new Internal::CommandMappingsPrivate(this))
 {