Rollup merge of #145535 - lolbinarycat:rustdoc-invalid_html_tags-svg-145529, r=GuillaumeGomez

make rustdoc::invalid_html_tags more robust

best reviewed a commit at a time.

I kept finding more edge case so I ended up having to make quite significant changes to the parser in order to make it preserve state across events and handle multiline attributes correctly.

fixes rust-lang/rust#145529

Author: Zalathar