[css-align] definition of 'align-content'/'justify-content' should define computed value for 'auto'

https://drafts.csswg.org/css-align/#content-distribution says:

  # Name:                 justify-content, align-content
  # Computed value:       specified value, except for auto (see prose) 

The prose goes on to say that for flex containers, 'auto' computes
to 'stretch', and for grid containers, 'auto' computes to 'start'.
However, it doesn't explicitly say that in all other cases (block
containers, multicol layout, and elements to which the property
doesn't apply) the computed value for 'auto' is 'auto'.

-David

-- 
𝄞   L. David Baron                         http://dbaron.org/   𝄂
𝄢   Mozilla                          https://www.mozilla.org/   𝄂
             Before I built a wall I'd ask to know
             What I was walling in or walling out,
             And to whom I was like to give offense.
               - Robert Frost, Mending Wall (1914)