Auto merge of #7962 - Jarcho:fix_match_type_on_diagnostic_items, r=llogiq

Fix and improve `match_type_on_diagnostic_item`

This extracts the fix for the lint out of #7647. There's still a couple of other functions to check, but at least this will get lint working again.

The two added util functions (`is_diagnostic_item` and `is_lang_item`) are needed to handle `DefId` for unit and tuple struct/variant constructors. The `rustc_diagnostic_item` and `lang` attributes are attached to the struct/variant `DefId`, but most of the time they are used through their constructors which have a different `DefId`. The two utility functions will check if the `DefId` is for a constructor and switch to the associated struct/variant `DefId`.

There does seem to be a bug on rustc's side where constructor `DefId`s from external crates seem to be returning `DefKind::Variant` instead of `DefKind::Ctor()`. There's a workaround put in right.

changelog: None

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