Move internal modules to “internal” folder.

.internal/setData.js

@@ -0,0 +1,20 @@
+import baseSetData from './.internal/baseSetData.js';
+import shortOut from './.internal/shortOut.js';
+
+/**
+ * Sets metadata for `func`.
+ *
+ * **Note:** If this function becomes hot, i.e. is invoked a lot in a short
+ * period of time, it will trip its breaker and transition to an identity
+ * function to avoid garbage collection pauses in V8. See
+ * [V8 issue 2070](https://bugs.chromium.org/p/v8/issues/detail?id=2070)
+ * for more details.
+ *
+ * @private
+ * @param {Function} func The function to associate metadata with.
+ * @param {*} data The metadata.
+ * @returns {Function} Returns `func`.
+ */
+const setData = shortOut(baseSetData);
+
+export default setData;