Make Compiler::sess private.

Like `Compiler::codegen_backend`.

compiler/rustc_interface/src/interface.rs

@@ -38,7 +38,7 @@ pub type Result<T> = result::Result<T, ErrorGuaranteed>;
 /// Can be used to run `rustc_interface` queries.
 /// Created by passing [`Config`] to [`run_compiler`].
 pub struct Compiler {
-    pub(crate) sess: Session,
+    sess: Session,
     codegen_backend: Box<dyn CodegenBackend>,
     pub(crate) override_queries: Option<fn(&Session, &mut Providers)>,
 }

compiler/rustc_interface/src/queries.rs

@@ -102,7 +102,7 @@ impl<'tcx> Queries<'tcx> {
     }
 
     fn session(&self) -> &Session {
-        &self.compiler.sess
+        &self.compiler.session()
     }
 
     fn codegen_backend(&self) -> &dyn CodegenBackend {