test: bench private parsers

bench/parse now also times tidy's CSS, SCSS, Less, HTML, XML and
Handlebars parsers, against raffia, lightningcss, scraper, tl,
roxmltree, quick-xml and the handlebars crate. tidy keeps those parsers
private, so their entry points only build with --cfg tidy_bench, which
bench/parse sets. It isn't a feature, and without it the release tidy
binary is byte for byte the same.

bench/parse.ts runs it and writes bench/results/parse. --rejects lists
the files each tool rejects.