We should consider adding a sliver wrap widget. This widget would function like the Wrap widget, but support scrolling.

SliverGrid currently relies on users specifying a fixed cross axis count, or a max extent for the cross axis. Further, the only layout we support (SliverGridRegularTileLayout) assumes that the items in the grid are all the same size as well as evenly spaced.

Adding a SliverWrap widget could provide a lot more flexibility for users' layouts.