[css-flexbox] Should clarify if aspect ratio calculations use border-box or content-box #5246

E.g. here:
https://drafts.csswg.org/css-flexbox/#min-size-auto

The transferred size uses the aspect ratio, but it's not clear whether it should use the content box or border box for the calculation.

Also, here:
https://drafts.csswg.org/css-flexbox/#algo-main-item
the calculation says explicitly that the inner cross size is used, which contradicts https://drafts.csswg.org/css-sizing-4/#valdef-aspect-ratio-ratio which says that box-sizing determines whether to use content-box or border-box