bug#33532: 26.1; set-window-configuration does not restore display start

[Juri Linkov]

>> What do you think about implementing the same behavior for
>> markers like it's implemented by 'comint-move-point-for-output'?
>> I.e. the same way as 'comint-move-point-for-output' moves point
>> to the end of the output, after erasing the buffer markers could
>> move their positions towards their previous valid position until
>> there is enough reverted text that they reach the old position.
>> 
>> This is straightforward to implement.
>
> Is it?  Then perhaps I don't understand what "this" is, because
> support for keeping the markers' positions is implemented on the C
> level, and every insertion/deletion primitive runs the low-level code
> which implements that.  I wouldn't call changes in that area
> "straightforward" at all.

Straightforward because I thought it could reuse the existing
implementation of `insertion_type' that moves the marker
after text insertion.  Maybe I'm mistaken.