QmlJSPlugin: reorganize setup

Pimpl, remove use of global object pool, cosmetics, ...

Change-Id: I9e1415b07d7ff8e95db0998c87ce7d75ca638a8e
Reviewed-by: Marco Benelli <marco.benelli@qt.io>

src/plugins/qmljstools/qmljslocatordata.cpp

@@ -36,8 +36,7 @@ using namespace QmlJSTools::Internal;
 using namespace QmlJS;
 using namespace QmlJS::AST;
 
-LocatorData::LocatorData(QObject *parent)
-    : QObject(parent)
+LocatorData::LocatorData()
 {
     ModelManagerInterface *manager = ModelManagerInterface::instance();