Make CompilationFiles struct public for crates.io users

[est31]

The CompilationFiles struct contains metadata/target_short_hash methods to obtain metadata that is used as postfix for filenames of rlib files. This info is very relevant for the binary-dep-depinfo based cargo-udeps backend. It is exposed only to crates.io users via parsing the CLI args passed via the Executor trait but only if the compilation is actually done. In rerun scenarios where dependencies are still fresh, the executor trait is not used. Therefore, could CompilationFiles maybe be made public? Thanks.

See https://github.com/est31/cargo-udeps/blob/ee91e4710b8519b742b61301f9ccddebeaeaeed8/src/lib.rs#L379

[epage]

As a heads up, we've been talking about changing the layout of the target directory for #5931.

I'd be hesitant to expose these APIs for people to be operating on these files if we haven't stabilized the layout..

[est31]

cargo-udeps doesn't operate on these files at all, they are never written or read. cargo-udeps only uses these in comparisons of the file name.