Debugger: Replace debuggerCore() by equivalent free functions

One indirection less on the user code side, and easier to export
if needed (partially addressing QTCREATORBUG-13187)

Change-Id: I13ab9f471a3a34da7a6331aefc83f6d02413bfab
Reviewed-by: David Schulz <david.schulz@digia.com>

src/plugins/debugger/qml/qmlengine.cpp

@@ -83,7 +83,7 @@ namespace Internal {
 
 static QTreeView *inspectorTreeView()
 {
-    return DebuggerCore::inspectorView();
+    return Internal::inspectorView();
 }
 
 class ASTWalker : public Visitor