Part: CountSubShapesRecursive should be a TopoShape static function

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Problem description

At least in Part/Gui/Command - possibly in other places there is the need to count subshapes in a compound TopoDS_Shape (recursively! not just top level)

this has previously been implemented multiple times leading to code duplication - see #17468

This issue is open to mark the need to abstract this function and provide a feature as outlined by @wwmayer in https://github.com/FreeCAD/FreeCAD/pull/17469#discussion_r1816524908

then find any place in the code that counts subshapes and use it.

should probably be able to accept both TopoDS_Shape and TopoShapes (but that's trivial)

### Full version info

```shell
main
```

### Subproject(s) affected?

Part

### Anything else?

_No response_

### Code of Conduct

- [X] I agree to follow this project's Code of Conduct