bug#59935: 29.0.60; project-list-buffers is slow

[Juri Linkov <juri@linkov.net>]

> Here's an idea: when 'list-buffers-noselect' received a plain list of
> buffers in its BUFFER-LIST argument, it doesn't save that anywhere.
>
> That seems like a bug, doesn't it? That hitting 'g' in such a buffer-list
> buffer resets its contents to all buffer (except hidden, etc).
>
> So it probably makes sense to save it as well.
>
> Long story short, I suggest to name the new variable
> Buffer-menu-buffer-list, and save the value of the BUFFER-LIST argument to
> it no matter what. And, likewise, use it. But when the value is a function,
> call it to obtain the actual list.

Thanks for the idea.  Implemented in the commit a99d0e7e6c9.

> One side-effect of this, though, is that the BUFFER-LIST argument to
> list-buffers--refresh will have no purpose anymore.

I'm not sure about removing the old argument BUFFER-LIST from
list-buffers--refresh, even though it's an internal function.

It also has another argument OLD-BUFFER that could be turned later
into buffer-local, to keep the current buffer marker after revert.