Make the main window resizeable on Linux

[Sébastien Duquette (ekse)]

The main window was not resizeable because the X11 Avalonia backend treats WindowDecorations.BorderOnly as WindowDecorations.None. This change implements resize grips on the window.

2026-05-02.21-41-16.mp4

[Marc-André Moreau (mamoreau-devolutions)]

I'd just want to make sure that this doesn't affect WSL usage - there's a runtime check for WSL to adapt it and avoid some issues: #4580

For regular Linux we can leave native decorations enabled but for WSLg it wouldn't get sized and maximized properly. Disabling decorations to get them from the Windows size instead worked better

Runtime checks for WSL are fine to adapt between the two

[Sébastien Duquette (ekse)]

I'd just want to make sure that this doesn't affect WSL usage - there's a runtime check for WSL to adapt it and avoid some issues: #4580

For regular Linux we can leave native decorations enabled but for WSLg it wouldn't get sized and maximized properly. Disabling decorations to get them from the Windows size instead worked better

Runtime checks for WSL are fine to adapt between the two

This is taken into account, the border grips are enabled only when isWsl is false. (see https://github.com/Devolutions/UniGetUI/pull/4675/changes#diff-133754dff4c1cb9804c5fabcde40f72eb6a6c36bc32e2e3bcd175e50f5f3a963R211-R214)