absorb: only track absorb history on drag-n-drop success

Summary:
Dragging can fail because of invalid drop targets. Ensure the undo history only
tracks successful DnDs.

Reviewed By: evangrayk

Differential Revision: D67927312

fbshipit-source-id: 472f902581384d99e10770a25bc9ba565ee54ea0

addons/isl/src/stackEdit/ui/AbsorbStackEditPanel.tsx

@@ -318,6 +318,9 @@ function SingleAbsorbEdit(props: {edit: AbsorbEdit; inDraggingOverlay?: boolean}
         try {
           newStack = stack.setAbsorbEditDestination(fileStackIndex, absorbEditId, rev);
           writeAtom(draggingHint, null);
+          // `handleDrag` won't be updated with "refreshed" `stackEdit`.
+          // So `push` can work like `replaceTopOperation` while dragging.
+          stackEdit.push(newStack, {name: 'absorbMove', commit});
         } catch {
           writeAtom(
             draggingHint,
@@ -326,11 +329,6 @@ function SingleAbsorbEdit(props: {edit: AbsorbEdit; inDraggingOverlay?: boolean}
             ),
           );
         }
-        if (isDragging == null) {
-          stackEdit.push(newStack, {name: 'absorbMove', commit});
-        } else {
-          stackEdit.replaceTopOperation(newStack, {name: 'absorbMove', commit});
-        }
       }
     } else {
       // Ensure the hint is cleared when not dragging.