rust stdlib analysis contains absolute paths from appveyor and travis-CI

[staktrace]

Running something like rustup component add rust-analysis will download a tarball containing the -Zsave-analysis data for the rust stdlib crates. However, these JSON files in some cases contain absolute paths for the environment they were generated in, like /Users/travis/.cargo/registry/src/github.com-1ecc6299db9ec823/libc-0.2.46/src/unix/mod.rs or similar windows paths at C:\Users\appveyor, or other absolute paths like /cargo/registry/src/github.com-1ecc6299db9ec823/rustc-demangle-0.1.10/src/lib.rs. It would be better if the analysis data had relative paths so that the analysis files can be used on other machines.

See also rust-lang/rls#1339, /cc @Xanewok

[Xanewok]

I believe we can use --remap-path-prefix to fix that.

Now we encode some of the paths (which are represented as PathBufs in rls-data see #60053 (comment)) as a byte vector, so it'd be also good for #60053 to land so we can see how much of the paths are affected.

[jyn514]

The compiler should be using /rustc/<long hash> for these paths consistently since #83813.

[jyn514]

Save-analysis has been removed from the compiler.