Auto merge of #7504 - flip1995:rename-lints, r=flip1995

Rename two lints to comply with our lint naming convention

self_named_constructor -> self_named_constructors
append_instead_of_extend -> extend_with_drain

We don't need to `register_renamed` those lints, since I'll backport them to beta, so the old names won't hit stable.

changelog: none
(I'll adapt the changelog before merging #7498)