getDeclaredVariables(node) {
        return this.__declaredVariables.get(node) || [];
    }
Get variables that are declared by the node.

"are declared by the node" means the node is same as `Variable.defs[].node` or `Variable.defs[].parent`.
If the node declares nothing, this method returns an empty array.
CAUTION: This API is experimental. See https://github.com/estools/escope/pull/69 for more details.
@param {Espree.Node} node a node to get.
@returns {Variable[]} variables that declared by the node.