3920: Implement expand_task and list_macros in proc_macro_srv r=matklad a=edwin0cheng
This PR finish up the remain `proc_macro_srv` implementation :
1. Added dylib loading code for proc-macro crate dylib. Note that we have to add some special flags for unix loading because of a bug in old version of glibc, see https://github.com/fedochet/rust-proc-macro-panic-inside-panic-expample/issues/1 and https://github.com/rust-lang/rust/issues/60593 for details.
2. Added tests for proc-macro expansion: We use a trick here by adding `serde_derive` to dev-dependencies and calling `cargo-metadata` for searching its dylib path, and expand it in our tests.
[EDIT]
Note that this PR **DO NOT** implement the final glue code with rust-analzyer and proc-macro-srv yet.
Co-authored-by: Edwin Cheng <edwin0cheng@gmail.com>
0ecdba20df