function getWriteExpr(reference) {
	if (reference.writeExpr) {
		return reference.writeExpr;
	}
	let node = reference.identifier;

	while (node) {
		const t = node.parent.type;

		if (t === "AssignmentExpression" && node.parent.left === node) {
			return node.parent.right;
		}
		if (t === "MemberExpression" && node.parent.object === node) {
			node = node.parent;
			continue;
		}

		break;
	}

	return null;
}
Get `reference.writeExpr` of a given reference.
If it's the read reference of MemberExpression in LHS, returns RHS in order to address `a.b = await a`
@param {escope.Reference} reference The reference to get.
@returns {Expression|null} The `reference.writeExpr`.