Desktop Icons: More various changes

FolderView: Update perStripe on relativeScreenRect changes

We never updated the perStripe properly on geometry changes, until after moving an item. This caused issues where the range selection would highlight wrong items.

Using relativeScreenRectChanges here allows us to react to panels too.

Positioner: Fix the order of operations

In case the positions data here would be wrong, we would reset the model and then return, which causes a broken model.

Instead, return early.

FolderView: Fix regression with loadAndApplyPositionsConfig desync

Calling loadAndApplyPositionsConfig will cause desync here.

It's better to have the icons a bit scattered when changing display scaling, than have the whole coordinate system out of sync.