Move internal modules to “internal” folder.

.internal/root.js

@@ -0,0 +1,9 @@
+import freeGlobal from './.internal/freeGlobal.js';
+
+/** Detect free variable `self`. */
+const freeSelf = typeof self == 'object' && self && self.Object === Object && self;
+
+/** Used as a reference to the global object. */
+const root = freeGlobal || freeSelf || Function('return this')();
+
+export default root;