bug#62352: Very slow scroll-down-line with a lot of text properties

[Herman, Geza]

Emacs can freeze for seconds when scroll-down-line is called multiple 
times if the buffer contains a lot of text properties.

I noticed this when using lsp-mode for C++.

To reproduce the issue without lsp-mode, execute this elisp command with 
M-:, this will add a face to operators:

(font-lock-add-keywords 'c++-mode '(("[][~!^&\|<>:=,.\\+*/%-]" 0 'error)))

Also, bind scroll-down-line to a key, like shift-up:

(global-set-key (kbd "<S-up>") 'scroll-down-line)

Then, put the attached example.cpp into a c++ buffer, move the point to 
the bottom, then press and hold shift-up. Emacs will update the window 
for several scroll events, but after that it won't update the screen for 
a while. Even after shift-up is released, Emacs needs several seconds to 
be interactive again.


In GNU Emacs 29.0.60 (build 1, x86_64-pc-linux-gnu, GTK+ Version
 3.24.36, cairo version 1.16.0) of 2023-03-21 built on okoska
Repository revision: 7a1272168af1a5b82979efa29451147c5d867981
Repository branch: emacs-29
Windowing system distributor 'The X.Org Foundation', version 11.0.12101006
System Description: Debian GNU/Linux bookworm/sid

Configured using:
 'configure --with-native-compilation=aot --without-compress-install
 --with-json --with-xinput2 --with-xwidgets --with-tree-sitter
 --with-cairo'

Configured features:
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TIFF TOOLKIT_SCROLL_BARS TREE_SITTER WEBP X11 XDBE XIM XINPUT2 XPM
XWIDGETS GTK3 ZLIB

Important settings:
  value of $LC_ALL: C.UTF-8
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Major mode: C++//l

Minor modes in effect:
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  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  abbrev-mode: t

Load-path shadows:
/home/geza/.emacs.d/elpa/transient-20230304.1149/transient hides 
/usr/local/share/emacs/29.0.60/lisp/transient

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Memory information:
((conses 16 150387 10063)
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 (string-bytes 1 1406757)
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example.cpp
Description: Text Data