Tweaks to left pane snapping logic

ts/util/isSorted.ts

@@ -0,0 +1,13 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+export function isSorted(list: Iterable<number>): boolean {
+  let previousItem: undefined | number;
+  for (const item of list) {
+    if (previousItem !== undefined && item < previousItem) {
+      return false;
+    }
+    previousItem = item;
+  }
+  return true;
+}