RLS save-analysis is gone, need some other way to inspect crates

[wfraser]

The -Z save-analysis feature was removed in rust-lang/rust#101841 which completely breaks this program's method of inspecting crates. nightly-2023-02-15 (1.69.0) I think is the last nightly to support this code.

The mentioned recommended alternatives involve using rust-analyzer, which is sub-optimal because the entire point of this tool is to show you how rustc sees things, and r-a is a separate implementation and is imperfect in its analysis.

Maybe I could make a compiler driver similar to how rustdoc works, but it'll be a lot of work and probably very fragile :(