bug#29713: 26.0; Provide completion for `make-frame-on-display'

[Juri Linkov]

>>> Maybe it could use `x-display-list'.  But I don't know how portable it is.
>>> Is `x-display-list' available on OSX and Windows?
>>
>> It's not available on --without-x builds:
>>
>> 0. ./src/emacs -Q
>> 1. M-x toggle-debug-on-error RET
>> 2. M-x make-frame-on-display RET
>>    Debugger entered--Lisp error: (void-function x-display-list)
>>
>> What's TRT here?
>
> Maybe fall back to previous implementation replaced by x-display-list
> in 0746a9e275d, i.e.
>
>   (if (fboundp 'x-display-list)
>       (x-display-list)
>     (delete-dups
>      (mapcar (lambda (frame)
>                (frame-parameter frame 'display))
>              (frame-list))))

Or maybe better to fall back to 'make-frame'?
I.e. don't signal an error, don't ask a question,
just create a new frame on the current display.

So on --without-x builds, make-frame-on-display
could be like an alias to make-frame.