Rollup of 10 pull requests

[Centril]

Successful merges:

• Stabilize todo macro #61879 (Stabilize todo macro)
• Deprecate #![plugin] & #[plugin_registrar] #64675 (Deprecate #![plugin] & #[plugin_registrar])
• add regression test for #60218 #64706 (add regression test for ICE on higher-trait bounds #60218)
• Prevent rustdoc feature doctests #64741 (Prevent rustdoc feature doctests)
• Replace mentions of IRC with Discord #65004 (Replace mentions of IRC with Discord)
• Always mark rust and rust-call abi's as unwind #65020 (Always mark rust and rust-call abi's as unwind)
• metadata: Some crate loading cleanup #65026 (metadata: Some crate loading cleanup)
• Add long error explanation for E0556 #65055 (Add long error explanation for E0556)
• Make visit projection iterative #65056 (Make visit projection iterative)
• typo: fix typo in E0392 #65057 (typo: fix typo in E0392)

Failed merges:

r? @ghost