Fix disruption of windows' display by shr.el

Fix disruption of windows' display by shr.el

* src/window.c (struct saved_window): New member 'vscroll'.
(Fset_window_configuration, save_window_save): Save and restore
the window's vscroll value.

* lisp/net/shr.el (shr-insert-document): Restore the original
window's hscroll, in case we are rendering in a window other than
where the document will be eventually displayed.  This avoids
resetting hscroll of windows we use temporarily for shr's
rendering job.  (Bug#56008)