Native file manager not used on Linux

[HaivuUK]

Summary

Slicer uses the native file manager on other platforms, and the QtFileDialog was depreciated as per PR #5674. However, on Linux the old behaviour is still present. This limits the ability to use network drives or other non-main storage.

Steps to reproduce

Actual Behaviour

• Run Slicer official distribution.
• Attempt to add data.
• Browse.
• QtFileDialog is opened.

Expected Behaviour

• Run Slicer official distribution.
• Attempt to add data.
• Browse.
• Dolphin or Nautilus file dialogue is opened.

Environment

• Slicer version: Slicer-5.6.1-2023-12-12 & Slicer-5.7.0-2024-04-03
• Operating system: Linux (tested on Ubuntu and Fedora)