Auto merge of #50879 - petrochenkov:lintconv, r=nikomatsakis

Fix naming conventions for new lints

We actually have an RFC from Oct 2014 specifying naming conventions for lints that is still relevant - https://github.com/rust-lang/rfcs/blob/master/text/0344-conventions-galore.md#lints.
Unfortunately, human memory doesn't work for such prolonged periods of time, so a number of recently added edition-related lints don't follow the conventions.
This PR fixes names for those lints.

Unstable lints, simply renamed:
- `unused_lifetime` -> `unused_lifetimes`
- `absolute_path_not_starting_with_crate` -> `absolute_paths_not_starting_with_crate`
- `unnecessary_extern_crate` -> `unnecessary_extern_crates`

New lints stabilized in the last couple of releases, registered as renamed (old names still work with a warning):
- `single_use_lifetime` -> `single_use_lifetimes`
- `elided_lifetime_in_path` -> `elided_lifetimes_in_paths`
- `bare_trait_object` -> `bare_trait_objects`
- `unstable_name_collision` -> `unstable_name_collisions`
- `unused_doc_comment` -> `unused_doc_comments`

NOT changed, too old to rename:
- `const_err` -> `const_errors`
- `unused_allocation` -> `unused_allocations`

NOT changed, deprecation lints, no need to rename, they are going to be removed anyway:
- `invalid_type_param_default` -> `invalid_type_param_defaults`
- `missing_fragment_specifier` -> `missing_fragment_specifiers`
- `tyvar_behind_raw_pointer` -> `tyvars_behind_raw_pointer`
- `illegal_floating_point_literal_pattern` -> `illegal_floating_point_literal_patterns`

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