bug#50178: 28.0.50; Size of echo area does not account for line-spacing

[martin rudalics]

>> It must know and handle every setting that affects line height, current
>> and future. It would be handy if Emacs provided a function that does
>> that.
>
> We already have it: window-text-pixel-size.

To elaborate:

(1) You first have to calculate the maximum permissible pixel height of
    the echo area window from the character height of the frame where
    you intend to display the completions and the value of
    `max-mini-window-height' height as specified for that frame.  Note
    that for a minibuffer-less frame the echo area window may appear on
    another frame whose character height you have to use here.

(2) You then have to calculate the pixel height of each completion line
    as if it were shown in the echo area window mentioned in (1) using
    `window-text-pixel-size' and add it to some cumulative height until
    you have exhausted the maximum permissible height calculated in (1).

martin