rust-analyzer does not really attempt to be backwards compatible, so
when users opt-into the component a toolchain override, we should prefer
that over any other rust-analyzer (especially our own) for better
toolchain compatibility in case people have a more out of date install.
This mirrors the VSCode extension behavior

Release Notes:

- When a worktree contains a Rust toolchain file with a rust analyzer
component specified, Zed will now spawn the given toolchain's
rust-analyzer for toolchain compatability