Move internal modules to “internal” folder.

.internal/getMapData.js

@@ -0,0 +1,18 @@
+import isKeyable from './.internal/isKeyable.js';
+
+/**
+ * Gets the data for `map`.
+ *
+ * @private
+ * @param {Object} map The map to query.
+ * @param {string} key The reference key.
+ * @returns {*} Returns the map data.
+ */
+function getMapData({ __data__ }, key) {
+  const data = __data__;
+  return isKeyable(key)
+    ? data[typeof key == 'string' ? 'string' : 'hash']
+    : data.map;
+}
+
+export default getMapData;