texi2any is too slow because of Unicode::Collate

[Gavin Smith]

I found that texi2any was significantly slower than expected on a
manual.

I ran with Devel::NYTProf:

TEXINFO_XS=require perl -d:NYTProf ../texi2any.pl 
../../../emacs-lispref-27.2/elisp.texi

The flame graph output shows that 75% of the execution time is spent in
Texinfo::Convert::Info::format_printindex, and 70% within
Unicode::Collate::cmp.  Here are the top functions:


Top 15 Subroutines
Calls   P  F Exc   Inc      Subroutine
2280071 1  1 23.1s 25.5s    Unicode::Collate::getWt
122770  1  1 14.4s 15.6s    Unicode::Collate::splitEnt
351998  22 1 7.86s 67.2s    Texinfo::Convert::Plaintext::_convert
122770  1  1 6.86s 48.8s    Unicode::Collate::getSortKey
270366  28 1 1.52s 1.59s    Texinfo::Convert::Plaintext::_count_added
2280071 1  1 973ms 973ms    Unicode::Collate::varCE (xsub)
167542  1  1 899ms 1.26s    Texinfo::Convert::Plaintext::_process_text
184832  8  2 842ms 842ms    Texinfo::Convert::Paragraph::add_text (xsub)
2280071 1  1 724ms 724ms    Unicode::Collate::_fetch_simple (xsub)
2280071 1  1 550ms 550ms    Unicode::Collate::_ignorable_simple (xsub)
4564446 8  1 530ms 530ms    Unicode::Collate::CORE:match (opcode)
2280071 1  1 508ms 508ms    Unicode::Collate::_exists_simple (xsub)
62010   1  1 463ms 49.7s    Texinfo::Structuring::_collator_sort_string
122770  1  1 444ms 622ms    Unicode::Collate::process
1       1  1 434ms 434ms    Texinfo::Parser::parse_file (xsub)


Can we avoid using Unicode::Collate as much?