Rollup merge of #151558 - mejrs:port_on_unimplemented, r=jdonszelmann,jonathanbrouwer

Port diagnostic attributes

*[View all comments](https://triagebot.infra.rust-lang.org/gh-comments/rust-lang/rust/pull/151558)*

Ports all the diagnostic attributes: on_const, on_unimplemented and rustc_on_unimplemented.

I thought about migrating them one by one but that would leave a lot of code duplicated. So this PR looks big but it's mostly a lot of moving code around with slight modifications.

r? @JonathanBrouwer

cc @jdonszelmann feel free to review if you want, not sure which of you wants it.

Author: JonathanBrouwer