bug#34516: Multi-monitor frame sets

[Juri Linkov]

>>>> Since on Windows 'display-monitor-attributes-list' returns such
>>>> fake monitor names:
>>>>
>>>>   \\.\DISPLAY1
>>>>   \\.\DISPLAY2
>>>>
>>>> on macOS it could return something like that or generate fake names
>>>> from geometry like "1920x1080+0+0", "2560x1440+1920+16".
>>>
>>> I often have two identical monitors attached, so that would be
>>> confusing :-)
>>>
>>> Something like this (assuming nobody every connects more than 9
>>> monitors to the same system).
>>
>> I hope at least the primary monitor always comes first in the list.
>
> The `display-monitor-attributes-list' docstring states:
>
> "Return a list of physical monitor attributes on DISPLAY.
> DISPLAY can be a display name, a terminal name, or a frame.
> If DISPLAY is omitted or nil, it defaults to the selected frame’s display.
> Each element of the list represents the attributes of a physical
> monitor.  The first element corresponds to the primary monitor."
>           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> Why are you still guessing, instead of reading the documentation ?

Right, the documentation should be the ultimate source of truth.
So I committed the patch to master.