LSP: set completion trigger characters to assist provider

Change-Id: I39bd9aca77d824b6533ea8e4c3aa704b9112be45
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/plugins/languageclient/client.cpp

@@ -289,6 +289,11 @@ bool Client::openDocument(Core::IDocument *document)
     if (textDocument) {
         textDocument->completionAssistProvider();
         m_resetAssistProvider << textDocument;
+        m_completionProvider.setTriggerCharacters(
+            m_serverCapabilities.completionProvider()
+                .value_or(ServerCapabilities::CompletionOptions())
+                .triggerCharacters()
+                .value_or(QList<QString>()));
         textDocument->setCompletionAssistProvider(&m_completionProvider);
         textDocument->setQuickFixAssistProvider(&m_quickFixProvider);
         connect(textDocument, &QObject::destroyed, this, [this, textDocument]{