QmlJSEditorPlugin: Refactor

This follows the recently introduced pattern for plugin setup
- Pimpl QmlJSEditorPlugin
- remove unneeded uses of global object pool
- apply "static pattern"
- simplify some constructors of data members in some cases
- use in-class initialization in some case

Change-Id: I95b42d0885f4a8d6c9bfe1e4c004d3ace0a3eba5
Reviewed-by: Marco Benelli <marco.benelli@qt.io>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/qmljseditor/qmljsquickfixassist.cpp

@@ -80,12 +80,6 @@ class QmlJSQuickFixAssistProcessor : public IAssistProcessor
 // ---------------------------
 // QmlJSQuickFixAssistProvider
 // ---------------------------
-QmlJSQuickFixAssistProvider::QmlJSQuickFixAssistProvider(QObject *parent)
-    : IAssistProvider(parent)
-{}
-
-QmlJSQuickFixAssistProvider::~QmlJSQuickFixAssistProvider()
-{}
 
 IAssistProvider::RunType QmlJSQuickFixAssistProvider::runType() const
 {