Unrolled build for #145535

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 #145529

Author: rust-timer

src/librustdoc/lib.rs

@@ -11,6 +11,7 @@
 #![feature(file_buffered)]
 #![feature(format_args_nl)]
 #![feature(if_let_guard)]
+#![feature(iter_advance_by)]
 #![feature(iter_intersperse)]
 #![feature(round_char_boundary)]
 #![feature(rustc_private)]