Move internal modules to “internal” folder.

.internal/baseIsNaN.js

@@ -0,0 +1,12 @@
+/**
+ * The base implementation of `isNaN` without support for number objects.
+ *
+ * @private
+ * @param {*} value The value to check.
+ * @returns {boolean} Returns `true` if `value` is `NaN`, else `false`.
+ */
+function baseIsNaN(value) {
+  return value !== value;
+}
+
+export default baseIsNaN;