Move internal modules to “internal” folder.

.internal/baseToPairs.js

@@ -0,0 +1,16 @@
+import arrayMap from './.internal/arrayMap.js';
+
+/**
+ * The base implementation of `toPairs` and `toPairsIn` which creates an array
+ * of key-value pairs for `object` corresponding to the property names of `props`.
+ *
+ * @private
+ * @param {Object} object The object to query.
+ * @param {Array} props The property names to get values for.
+ * @returns {Object} Returns the key-value pairs.
+ */
+function baseToPairs(object, props) {
+  return arrayMap(props, key => [key, object[key]]);
+}
+
+export default baseToPairs;