String getFunctionSignature(Symbol functionDefinition) {
        StringBuilder signature = new StringBuilder();
        Node definitionNode = functionDefinition.getNode();
        //signature.append(definitionNode.getText());
        Node it = definitionNode.getNextSibling();
        do {
            signature.append(it.getText());
            it = it.getNextSibling();
        } while(it != null && !it.isASTInstance(NL.class) && !it.isASTInstance(openLbrace.class));
        //signature.append(")");
        return signature.toString();
    }
Compute completion snippets for all the builtin ranking features using the signatures
in {@link BuiltInFunctions}.
integration/schema-language-server/language-server/src/main/java/ai/vespa/schemals/lsp/schema/completion/provider/RankingExpressionCompletion.java