Cleanup proc_macro config

In general, there should be no reason to call `.to_string_lossy`.
If you want to display the path, use `.display()`.
If you want to pass the path to an OS API (like std::process::Command)
than use `PathBuf` or `OsString`.

crates/rust-analyzer/src/world.rs

@@ -153,7 +153,7 @@ impl WorldState {
                 Err(err) => {
                     log::error!(
                         "Failed to run ra_proc_macro_srv from path {}, error: {:?}",
-                        path,
+                        path.display(),
                         err
                     );
                     ProcMacroClient::dummy()