bug#35592: Use display-buffer-in-direction for completion-like windows

[martin rudalics]

> Only a small plea: could you please add an alias ‘(direction . bottom)’
> as a shorthand for ‘(direction . below) (window . main)’
>
> Similarly:
> top = (direction . above) (window . main)
> bottom = (direction . below) (window . main)
> leftmost = (direction . left) (window . main)
> rightmost = (direction . right) (window . main)

Patch attached.  But notice that these semantically clash with what you
earlier wanted for 'split-window':

                    ((eq side 'above) 'top)
                    ((eq side 'below) 'bottom)
                
martin

display-buffer-in-direction.diff
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