public Node getPreviousSibling() {
        return getSibling(-1);
    }
Returns the previous sibling of this schema node.
A sibling node is a node that shares the same parent node. 

@return the previous sibling of this schema node, or null if there is no previous sibling
integration/schema-language-server/language-server/src/main/java/ai/vespa/schemals/tree/Node.java