bug#56767: New commands to split frame

[Juri Linkov]

>> Since we already have the commands to split the current window,
>> shouldn't we also have the commands to split the current frame:
>
> and may be you would like to add aliases, just like
>
> split-window-horizontally -> split-window-right,
> split-window-vertically -> split-window-below

The word "below" is not quite correct because
display-buffer-below-selected uses positioning
relative to the current window.  Whereas the
corresponding function the uses the absolute
positioning contains the word "bottom" in its name:
display-buffer-at-bottom.

So the right alias would be split-frame-at-bottom.

Also display-buffer-in-direction supports the word
"rightmost", so its counterpart alias would be
split-frame-at-rightmost.

Then why not add also split-frame-at-leftmost
and split-frame-at-top?