348ec37f52
No user visible changes expected. Similar to rBc355be6faeac, but for view items now instead of the view. Not much of the item code is ported to use it yet, it's actually a bit tricky for the most part. But just introducing the base class already allows me to start unifying the view item buttons (`uiButTreeRow` and `uiButGridTile`). This would be a nice improvement.