DynamicSizeList direction

[koox00]

Currently DynamicSizeList assumes we want to render the first item at the bottom (L759).
This makes it cumbersome for lists that should display the first item at the top, since we need to reverse the items prior to feeding them to the list (see mattermost/mattermost-webapp#8350).

I would like to propose adding a direction: upwards|downwards or maybe order: asc|desc prop to handle both cases.