fix: closes mochajs#5115 (mochajs#5116)

Eleventy wasn't being able to parse the JSDocs for the returned type
on the getFullErrorStack function. Defining it as a new type and then
referencing it on the function fixes the issue

Author: LcsK

lib/reporters/base.js

@@ -227,7 +227,7 @@ var generateDiff = (exports.generateDiff = function (actual, expected) {
  * @private
  * @param {Error} err
  * @param {Set<Error>} [seen]
- * @return {{ message: string, msg: string, stack: string }}
+ * @return {FullErrorStack}
  */
 var getFullErrorStack = function (err, seen) {
   if (seen && seen.has(err)) {
@@ -580,3 +580,12 @@ function sameType(a, b) {
 Base.consoleLog = consoleLog;
 
 Base.abstract = true;
+
+/**
+ * An object with all stack traces recursively mounted from each err.cause
+ * @memberof module:lib/reporters/base
+ * @typedef {Object} FullErrorStack
+ * @property {string} message
+ * @property {string} msg
+ * @property {string} stack
+ */