LanguageClient: Support markdown tool tips with Qt 5.14

Use Qt::MarkdownText if language server returns markdown and it was
built against Qt 5.14.

Change-Id: I75787cfcb32480cb37bc0dadc4be12d005005099
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/languageclient/client.cpp

@@ -222,7 +222,11 @@ static ClientCapabilities generateClientCapabilities()
     documentCapabilities.setCodeAction(codeActionCapabilities);
 
     TextDocumentClientCapabilities::HoverCapabilities hover;
+#if QT_VERSION >= QT_VERSION_CHECK(5, 14, 0)
+    hover.setContentFormat({MarkupKind::markdown, MarkupKind::plaintext});
+#else
     hover.setContentFormat({MarkupKind::plaintext});
+#endif
     hover.setDynamicRegistration(true);
     documentCapabilities.setHover(hover);