Auto merge of #58824 - euclio:intra-link-ambiguity, r=petrochenkov

overhaul intra-doc-link ambiguity warning

Fixes #52784.

- Makes the warning part of the `intra_doc_link_resolution_failure`
lint.
- Tightens the span to just the ambiguous link.
- Reports ambiguities across all three namespaces.
- Uses structured suggestions for disambiguation.
- Adds a test for the warnings.

r? @QuietMisdreavus

Author: bors