TextEditor: sync code completions in snippets

Update all identical snippet placeholder after selecting an item from
the completion proposal.

Change-Id: Iac4f4183c30517a8133269cc607edadce0c6bd23
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/texteditor/codeassist/codeassistant.cpp

@@ -350,6 +350,7 @@ void CodeAssistantPrivate::processProposalItem(AssistProposalItemInterface *prop
     destroyContext();
     if (!proposalItem->isSnippet())
         process();
+    m_editorWidget->encourageApply();
 }
 
 void CodeAssistantPrivate::handlePrefixExpansion(const QString &newPrefix)