Move internal modules to “internal” folder.

.internal/strictLastIndexOf.js

@@ -0,0 +1,21 @@
+/**
+ * A specialized version of `lastIndexOf` which performs strict equality
+ * comparisons of values, i.e. `===`.
+ *
+ * @private
+ * @param {Array} array The array to inspect.
+ * @param {*} value The value to search for.
+ * @param {number} fromIndex The index to search from.
+ * @returns {number} Returns the index of the matched value, else `-1`.
+ */
+function strictLastIndexOf(array, value, fromIndex) {
+  let index = fromIndex + 1;
+  while (index--) {
+    if (array[index] === value) {
+      return index;
+    }
+  }
+  return index;
+}
+
+export default strictLastIndexOf;