Move internal modules to “internal” folder.

.internal/baseClamp.js

@@ -0,0 +1,22 @@
+/**
+ * The base implementation of `clamp` which doesn't coerce arguments.
+ *
+ * @private
+ * @param {number} number The number to clamp.
+ * @param {number} [lower] The lower bound.
+ * @param {number} upper The upper bound.
+ * @returns {number} Returns the clamped number.
+ */
+function baseClamp(number, lower, upper) {
+  if (number === number) {
+    if (upper !== undefined) {
+      number = number <= upper ? number : upper;
+    }
+    if (lower !== undefined) {
+      number = number >= lower ? number : lower;
+    }
+  }
+  return number;
+}
+
+export default baseClamp;