Move internal modules to “internal” folder.

.internal/basePropertyDeep.js

@@ -0,0 +1,14 @@
+import baseGet from './.internal/baseGet.js';
+
+/**
+ * A specialized version of `baseProperty` which supports deep paths.
+ *
+ * @private
+ * @param {Array|string} path The path of the property to get.
+ * @returns {Function} Returns the new accessor function.
+ */
+function basePropertyDeep(path) {
+  return object => baseGet(object, path);
+}
+
+export default basePropertyDeep;