Fix the main window icon on Wayland

Description

On Wayland, calling setWindowIcon() to set the window icon is no longer supported, the correct way is to call setDesktopFileName() instead. The desktop file is then used to load the correct icon.

See https://doc.qt.io/qt-6/qguiapplication.html#desktopFileName-prop and https://community.kde.org/Guidelines_and_HOWTOs/Wayland_Porting_Notes#Application_Icon for more information.

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Before:

After

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have read the CONTRIBUTING guide.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

I provide my contribution under the terms of the license of this repository and I affirm the Developer Certificate of Origin.