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

[Eli Zaretskii <eliz@gnu.org>]

> From: Juri Linkov <juri@jurta.org>
> Cc: Markus Triska <triska@metalevel.at>,  Eli Zaretskii <eliz@gnu.org>,  33532@debbugs.gnu.org
> Date: Tue, 04 Dec 2018 00:59:29 +0200
> 
> 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.

Please also keep in mind that markers are the basis for other
important features, like overlays and conversion of character to byte
positions and vice versa.  We need to consider the implications on all
those features.