LSP: rerequest completion if contents change while processing

Task-number: QTCREATORBUG-21108
Change-Id: I6ca7920e7099dba0ba1bc953a2e6296bd86c1dc1
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/languageclient/languageclientcodeassist.cpp

@@ -219,6 +219,7 @@ public:
     LanguageClientCompletionAssistProcessor(BaseClient *client);
     TextEditor::IAssistProposal *perform(const TextEditor::AssistInterface *interface) override;
     bool running() override;
+    bool needsRestart() const override { return true; }
 
 private:
     void handleCompletionResponse(const Response<CompletionResult, LanguageClientNull> &response);