Auto merge of #115689 - Alexendoo:clippy-doc-comments, r=notriddle,Manishearth,flip1995

Reuse rustdoc's doc comment handling in Clippy

Moves `source_span_for_markdown_range` and `span_of_attrs` (renamed to `span_of_fragments`) to `rustc_resolve::rustdoc` so it can be used in Clippy

Fixes rust-lang/rust-clippy#10277
Fixes rust-lang/rust-clippy#5593
Fixes rust-lang/rust-clippy#10263
Fixes rust-lang/rust-clippy#2581

Author: bors