File dialog is too small for video picker

[robertknight]

The file picker currently has a hardcoded height of 25rem. This is too small for when we're displaying videos in the picker. Here there is only room for two and a half items:

The breadcrumbs and dialog title use up a lot of vertical space here, so we could free up some by re-arranging / altering those. However we should also just alter the height to use more vertical space if we have it.

[robertknight]

Another thing we could do for videos specifically is switch to a grid-like layout. We don't have a suitable component in our component library yet, so we'd have to make that first.