chore: fix completions in #[salsa::tracked] functions

[davidbarsky]

This change allows rust-analyzer (and, I assume RustRover) to provide accurate completions inside of a #[salsa::tracked] function. Previously, I'd comment out the #[salsa::tracked] annotation when writing a tracked function, but this PR removes the need for that workaround.

As @Veykril put it, the core issue is that rust-analyzer's mbe crate is not very error-resilient: we no longer pick the correct match arm of the macro_rules macro because the input doesn't match—mbe should pick the closest match instead of giving up, but until mbe supports that, this PR papers over a rust-analyzer weakness 🌟 it makes the macro more IDE friendly 🌟 !

(Credit goes to Lukas for the tip, explanation, and joke!)

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[codspeed-hq]

CodSpeed Performance Report

Merging #653 will not alter performance

_{Comparing davidbarsky:davidbarsky/fix-completions-in-salsa-tracked-fns (5f14bbd) with master (639fd29)}

Summary

✅ 9 untouched benchmarks

[Veykril]

Clearly I should not be the one to approve this but if we do this we ought to give the same treatment to setup_method_body

[davidbarsky]

Getting methods to work is a bit trickier: the "wrap the inner fn in a block" trick doesn't seem to be sufficient for methods, and I'm not enough of an expert on macros to figure that out. Can we make that a followup?