Auto merge of #7182 - mgacek8:wrong_self_convention_to__variant, r=flip1995

For `to_*` variant don't lint in trait impl taking `self` when non-`Copy` type

Lint name: `wrong_self_convention`.
It relaxes rules for `to_*` variant, so it doesn't lint in trait definitions and implementations anymore.
Although, non-`Copy` type implementing trait's `to_*` method taking
`self` feels not good (consumes ownership, so should be rather named `into_`), it would be better if this case was a pedantic lint (allow-by-default) instead.
More information in the discussion with `@flip1995` [here](https://github.com/rust-lang/rust-clippy/pull/7002#discussion_r627363450)

changelog: `wrong_self_convention`: For `to_*` variant don't lint in trait impl taking `self` when non-`Copy` type
r? `@flip1995`