VarSet: Drag-n-drop properties between Groups

### Problem description

Ability to hold left mouse button on a property and drag it into another group. Also, add ability to manually reorder items inside each group and reorder whole groups as well

### Workbench affected?

None

### Steps to reproduce

-

### Expected behavior

Basic UX works in varset data view

### Actual behavior

Useless selection happens when dragging items in the VarSet Data View

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

```shell
OS: Windows 11 build 26200
Architecture: x86_64
Version: 1.1.0rc3.20260223 (Git shallow)
Build date: 2026/02/23 23:43:19
Build type: Release
Branch: (HEAD detached at adf7760)
Hash: adf77600e2526bf02804524f0d1991ab1c534abe
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, IfcOpenShell 0.8.4, OCC 7.8.1
Locale: Russian/Russia (ru_RU)
Navigation Style/Orbit Style/Rotation Mode: CAD/Rounded Arcball/Window center
Stylesheet/Theme/QtStyle: FreeCAD.qss/FreeCAD Dark/
Logical DPI/Physical DPI/Pixel Ratio: 96/108.888/1
```

### Last known good version (optional)

```shell

```