Move internal modules to “internal” folder.

.internal/arrayIncludes.js

@@ -0,0 +1,17 @@
+import baseIndexOf from './.internal/baseIndexOf.js';
+
+/**
+ * A specialized version of `includes` for arrays without support for
+ * specifying an index to search from.
+ *
+ * @private
+ * @param {Array} [array] The array to inspect.
+ * @param {*} target The value to search for.
+ * @returns {boolean} Returns `true` if `target` is found, else `false`.
+ */
+function arrayIncludes(array, value) {
+  const length = array == null ? 0 : array.length;
+  return !!length && baseIndexOf(array, value, 0) > -1;
+}
+
+export default arrayIncludes;