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.