Feature/qt6 - Fix icons not showing up in the RvFileDialog on Windows (compared to Qt5)

[cedrik-fuoco-adsk]

Feature/qt6 - Fix icons not showing up in the RvFileDialog (compared to Qt5)

Linked issues

n/a

Summarize your change.

On Windows, I added a custom delegate for the QTreeView because it seems there is an issue (or changes in Qt 6) with the alternatingRowColors options in Qt 6's QAbstractItemView. The alternating background is painted over the icon which results in the missing icons.

The custom delegate paints the elements in this order:

1. Background
2. Highlights
3. Icon
4. Text

Describe the reason for the change.

After comparing the RvFileDialog between the Qt 5 and Qt 6 version of RV, the icons were still missing on Windows.

Describe what you have tested and on which operating system.

Windows

If possible, provide screenshots.