internal: vendor query-group-macro in rust-analyzer

[davidbarsky]

Dependency of #18964. This shouldn't land until we get a Salsa release out, which depends on fixing the powerpc build failures.

[davidbarsky]

I'll fix that unused warning tomorrow, but I feel like we should hold off on landing this until on Monday, at the easliest.

[davidbarsky]

I realized (and fixed, locally) why we were getting a dead code warning: the crates/query-group-macro/tests/logger_db.rs was now being compiled as its own test rather than its own module. I assume this has to do with this crate being migrated from its own, standalone thing to being part of a larger Cargo workspace.

[davidbarsky]

Alright, flattened the match expression and fixed the dead code warning. I'd like to squash those 3 commits into one before landing this, however.