Move internal modules to “internal” folder.

.internal/baseFindIndex.js

@@ -0,0 +1,23 @@
+/**
+ * The base implementation of `findIndex` and `findLastIndex`.
+ *
+ * @private
+ * @param {Array} array The array to inspect.
+ * @param {Function} predicate The function invoked per iteration.
+ * @param {number} fromIndex The index to search from.
+ * @param {boolean} [fromRight] Specify iterating from right to left.
+ * @returns {number} Returns the index of the matched value, else `-1`.
+ */
+function baseFindIndex(array, predicate, fromIndex, fromRight) {
+  const length = array.length;
+  let index = fromIndex + (fromRight ? 1 : -1);
+
+  while ((fromRight ? index-- : ++index < length)) {
+    if (predicate(array[index], index, array)) {
+      return index;
+    }
+  }
+  return -1;
+}
+
+export default baseFindIndex;