Implement a config override for the default #[cfg(test)] in cargo crates

Fixes crates which vanish when the 'test' cfg atom is set.

Fix #7243.
Fix #9203.
Fix #7225.

crates/project_model/src/lib.rs

@@ -41,7 +41,7 @@ pub use crate::{
     },
     project_json::{ProjectJson, ProjectJsonData},
     sysroot::Sysroot,
-    workspace::{PackageRoot, ProjectWorkspace},
+    workspace::{CfgOverrides, PackageRoot, ProjectWorkspace},
 };
 
 pub use proc_macro_api::ProcMacroClient;