bug#59381: Should xref--marker-ring be per-window?

[Juri Linkov]

> While using xref (xref-find-definitions and xref-find-references, etc)
> in separate windows, I hit M-, to pop the marker stack expecting that
> each window should have a separate stack.
>
> However, it seems that the entire emacs instance shares a single
> xref--marker ring.
>
> Could we have separate xref--marker-rings per window, or some
> configuration option to enable that?

Ideally, making an existing variable window-local should be as easy
as making it buffer-local, e.g.:

  (make-variable-buffer-local 'xref--history)
  ->
  (make-variable-window-local 'xref--history)

But we are not here so far.