bug#50951: 28.0.50; Urdu text is not displayed correctly

[Visuwesh]

[புதன் செப்டம்பர் 07, 2022] Eli Zaretskii wrote:

>> Date: Wed, 07 Sep 2022 15:18:21 +0900
>> From: YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp>
>> Cc: Eli Zaretskii <eliz@gnu.org>,
>>      larsi@gnus.org,
>>      50951@debbugs.gnu.org
>> 
>> Probably the following change will fix the problem:
>
> Thanks.  Rah Guzar, can you try one of these changes and see if they
> fix the problem?

Not sure about Rah Guzar, but it squashes bug#54646 for me.  Thank you
so very much, Yamamoto Mitsuharu!

With regards to the performance, my eyes say that patch no. 1 (i.e., the
one that patches src/hbfont.c) is slightly faster than patch no. 2 when
I continually zoomed to reproduce bug#54646.  The test material was this
random webpage https://www.dinamalar.com/news_detail.asp?id=3117719,
and M-x report-emacs-bug report on the Emacs with the patch is at the
end.
The test that I used is the same as I outlined in bug#54646, namely,
visit that webpage in eww, zoom in and out with C-scroll-wheel.  The
glyphs _do not_ bump into each other or get weirdly placed whereas
without the patch, glyphs can be oddly spaced.

In GNU Emacs 29.0.50 (build 6, x86_64-pc-linux-gnu, X toolkit, cairo
 version 1.16.0, Xaw scroll bars) of 2022-09-08 built on astatine
Repository revision: 9219e83b3c0ef53df02caf4c8ba38f482937ab50
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101004
System Description: Debian GNU/Linux bookworm/sid

Configured using:
 'configure --with-sound=alsa --with-x-toolkit=lucid --with-json
 --without-xaw3d --without-gconf --without-libsystemd'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LIBOTF LIBSELINUX LIBXML2 MODULES NOTIFY INOTIFY PDUMPER PNG RSVG
SECCOMP SOUND SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS WEBP X11 XDBE XIM
XINPUT2 XPM LUCID ZLIB

Important settings:
  value of $LC_MONETARY: ta_IN.UTF-8
  value of $LC_NUMERIC: ta_IN.UTF-8
  value of $LANG: en_GB.UTF-8
  locale-coding-system: utf-8-unix