PackedInt32Array handling in Editor is broken, SoftBody almost unusable.

### Tested versions

Reproducible: 4.3 mono stable, 4.4.dev2 mono
Working: 4.1 mono

### System information

Windows 7 - Godot 4.3 stable mono

### Issue description

Editing PackedInt32Array from the editor (SoftBody3D pinned points in this example) is fundamentally broken, changing any value other than the last removes the last entry. Clicking on the pinned points does nothing. This makes SoftBody barely usable.

Am I the only one having those issues or this have gone unnoticed somehow?

### Steps to reproduce

1. Make a SoftBody3D with 3 pinned points.
2. Change the first or second point's index.
OR
3. Click on any point in the 3D view to add it to the array - does not work.

### Minimal reproduction project (MRP)

[softbodyisbroken.zip](https://github.com/user-attachments/files/17048765/softbodyisbroken.zip)

Use the attached softbodyisbroken.zip project to reproduce the issue in the Godot Editor with a SoftBody3D and three pinned points. Inspect PackedInt32Array editing and the SoftBody3D pinned-point interaction in the 3D view; done means changing any entry preserves the array and clicking points adds them correctly.

Written by the indexing model from the issue text.