Rollup merge of #136400 - lolbinarycat:rustdoc-link-lint-135851, r=GuillaumeGomez

Improve handling of rustdoc lints when used with raw doc fragments.

1. `rustdoc::bare_urls` no longer outputs incoherent suggestions if `source_span_for_markdown_range` returns None, instead outputting no suggestion
2. `source_span_for_markdown_range` has one more heuristic, so it will return `None` less often.
3. add ui test to make sure we don't emit nonsense suggestions.

fixes rust-lang/rust#135851

Author: matthiaskrgr