bug#40808: 27.0.91; inaccuracy in isearch-lazy-count

[Juri Linkov]

>> Fine with me, but please make this change on master, not on emacs-27.
>
> Right decision, because org-mode is broken anyway, and this fix won't make
> it better.  A test case that demonstrates the problem in org-mode:
>
> 0. emacs -Q
> 1. visit emacs/etc/ORG-NEWS
> 2. isearch for "http": C-s http C-s C-s C-s ...
>
> it eventually stops at org links where "http" is invisible, such as
>
>   [[https://orgmode.org/worg/library-of-babel.html][here]]
>
> The problem is that org-mode puts the text property 'invisible'
> only when the link is scrolled into view, I guess it puts the property
> using font-lock.
>
> So at least in emacs-27 now it consistently counts all matches
> ignoring their visibility.

I'm still unsure about pushing this change.  The current state of things:

- in emacs-27 and master now it counts all matches, including invisible,
  regardless of the value of search-invisible;

- the proposed change for master doesn't include in the count these
  invisible matches that can't be visited by opening overlays;

- but this fix is pointless for org-mode where visiting invisible
  matches is broken, and where its count varies after visiting
  and opening hidden overlays.