bug#57245: 29.0.50; M-> in a large XML file (without long lines) is slow

[Dmitry Gutov]

Branching this off from the discussion in bug#56682.

Prerequisite: Have an XML file that is 20 MB in size, and doesn't have
long lines.

Or follow steps 1-3 to create one.

1. wget -o large-file.xml 
https://updates.drupal.org/release-history/drupal/current
2. M-% /> RET ^J/> RET (to break up the long line into smaller pieces)
3. Select the contents of the file and copy them over and over for 99
times. Alternatively, copy them 9 times, then select the result, and
copy it 9 times as well. Save the buffer.

(To try to keep XML valid -- not sure if necessary -- you can only
perform the copying operation on the contents of the <releases> tag. But
that's probably not important. I did that, though.)

4. Kill the buffer and re-visit it again. Press M->.
5. Note the delay.

Here's the profiler output:

        1397  95% - command-execute
        1397  95%  - call-interactively
        1338  91%   - funcall-interactively
        1331  90%    - end-of-buffer
        1327  90%     - recenter
        1327  90%      - jit-lock-function
        1327  90%       - jit-lock-fontify-now
        1327  90%        - jit-lock--run-functions
        1327  90%         - run-hook-wrapped
        1327  90%          - #<compiled -0x14ecf3ff276f01c3>
        1327  90%           - font-lock-fontify-region
        1327  90%            - font-lock-default-fontify-region
        1327  90%             - nxml-extend-region
         845  57%              - skip-syntax-forward
         845  57%               - internal--syntax-propertize
         845  57%                - syntax-propertize
         845  57%                 - nxml-syntax-propertize
         845  57%                  - sgml-syntax-propertize
         842  57%                   - #<compiled 0x1894bdc3ad4ca90>
         479  32%                      sgml--syntax-propertize-ppss
           3   0%                     syntax-ppss
         482  32%              - nxml-move-outside-backwards
         482  32%               - nxml-inside-start
         482  32%                  syntax-ppss
           7   0%    + execute-extended-command
          59   4%   + byte-code
          59   4% + ...
          10   0% + timer-event-handler


In GNU Emacs 29.0.50 (build 3, x86_64-pc-linux-gnu, GTK+ Version 
3.24.20, cairo version 1.16.0)
 of 2022-08-16 built on potemkin
Repository revision: 81ff64d3ca8d6e43e976f209399d2a0e9b4a7dd8
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12013000
System Description: Ubuntu 20.04.4 LTS