[css-flexbox][css-sizing] Move min-width and min-height partial definitions to css-sizing #1920

CSS Flexbox provides partial definitions of min-height and min-width with the new auto initial value.

This kind of things should not be allowed. How is someone looking for the initial value of these properties supposed to know that it's defined in Flexbox?

So I think these definitions should be moved to wherever makes sense. Probably this would be css-box, but it seems it has been abandoned. So css-sizing seems the best option.

Then css-sizing would define auto as the initial value, and say that it represents the "automatic minimum size" which, unless otherwise defined by the layout model, is 0. CSS Flexbox and CSS Grid should only define this automatic minimum size in their layouts.