Move internal modules to “internal” folder.

.internal/asciiSize.js

@@ -0,0 +1,12 @@
+import baseProperty from './.internal/baseProperty.js';
+
+/**
+ * Gets the size of an ASCII `string`.
+ *
+ * @private
+ * @param {string} string The string inspect.
+ * @returns {number} Returns the string size.
+ */
+const asciiSize = baseProperty('length');
+
+export default asciiSize;