QmlDesigner: Fix used imports not being in sync with model content

Figuring out the used imports checks all model nodes, which means
model needs to be updated before used imports are determined.
Fixed by moving setupUsedImports() call after model sync.

Fixes: QDS-4985
Change-Id: I3f03055d36cb638bcfcd48dc973dbae3af7d8002
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>

src/plugins/qmldesigner/designercore/model/texttomodelmerger.cpp

@@ -1099,7 +1099,6 @@ bool TextToModelMerger::load(const QString &data, DifferenceHandler &differenceH
                 m_rewriterView->setWarnings(warnings);
             qCInfo(rewriterBenchmark) << "checked semantic errors:" << time.elapsed();
         }
-        setupUsedImports();
 
         AST::UiObjectMember *astRootNode = nullptr;
         if (AST::UiProgram *program = m_document->qmlProgram())
@@ -1111,6 +1110,8 @@ bool TextToModelMerger::load(const QString &data, DifferenceHandler &differenceH
 
         qCInfo(rewriterBenchmark) << "synced nodes:" << time.elapsed();
 
+        setupUsedImports();
+
         setActive(false);
 
         return true;