function safelyShadowsUndefined(variable) {
	return (
		variable.name === "undefined" &&
		variable.references.every(ref => !ref.isWrite()) &&
		variable.defs.every(
			def =>
				def.node.type === "VariableDeclarator" &&
				def.node.init === null,
		)
	);
}
Determines if a variable safely shadows undefined.
This is the case when a variable named `undefined` is never assigned to a value (i.e. it always shares the same value
as the global).
@param {eslintScope.Variable} variable The variable to check
@returns {boolean} true if this variable safely shadows `undefined`