Link: Toggling visibility of a Link to a Body should show the tip if nothing was visible inside

### Problem description

The same thing was added for Bodies in:
* https://github.com/FreeCAD/FreeCAD/pull/24887

The same has to be added to Links to Bodies.

### Workbench affected?

Core (App, Gui,...)

### Steps to reproduce

na

### Expected behavior

na

### Actual behavior

na

### Development version About Info (in Safe Mode)

```shell
OS: Ubuntu 26.04 LTS (ubuntu:GNOME/ubuntu/wayland)
Architecture: x86_64
Version: 1.2.0dev.20260602 (Git shallow)
Build date: 2026/06/02 19:21:10
Build type: Release
Branch: (HEAD detached at 07de249ec)
Hash: 07de249ec749d3fba6710c78da8bca7c66243347
Python 3.11.14, Qt 6.8.3, Coin 4.0.3, Vtk 9.3.1, boost 1_86, Eigen3 3.4.0, PySide 6.8.3
shiboken 6.8.3, xerces-c 3.3.0, Clipper2 , IfcOpenShell 0.8.2, OCC 7.8.1
Locale: English/United States (en_US)
Stylesheet/Theme/QtStyle: OpenDark.qss/OpenDark/
Navigation Style/Orbit Style/Rotation Mode: Touchpad/Trackball/Drag at cursor
Logical DPI/Physical DPI/Pixel Ratio: 96/94.485/1
Installed mods:
* Assembly4 0.61.0
* Assembly4.1 0.61.0-0.2
* Cables Workbench 0.3.5
* Curves workbench 0.6.71
* DFM 0.1.2
* DFM 0.1.9
* Diff Tools Documentation 0.1.0
* Fasteners Workbench 0.5.51
* KicadStepUp Workbench 11.8.2
* Lattice2 Workbench 1.1.0
* OSH Automated Documentation 0.2.3
* OpenTheme 2025.5.20
* Render 2024.12.15
* SheetMetal Workbench 0.8.10
```

### Last known good version (optional)

```shell

```

Start by reading the behavior added for Bodies in pull request 24887, then locate the corresponding visibility handling for Links to Bodies in the Core App/Gui code. Reproduce the case where no content is visible and toggle the Link visibility. Done means the same tip shown for Bodies appears for a Link to a Body when nothing inside it was visible.

Written by the indexing model from the issue text.