Auto merge of #13664 - epage:refactor-toml, r=weihanglo

fix(toml): Warn on unused workspace.dependencies keys on virtual workspaces

### What does this PR try to resolve?

This splits out refactors that build on #13589 in preparation for resolving #13456.

As part of those refactors, I noticed an inconsistency on when we warn for unused keys.  We have parallel code paths between `to_virtual_manifest` and `to_real_manifest` and only one got updated on a change.  This syncs them up.  Hopefully the end state this builds to will reduce duplication.

### How should we test and review this PR?

### Additional information

src/cargo/core/manifest.rs

@@ -28,6 +28,12 @@ pub enum EitherManifest {
 }
 
 impl EitherManifest {
+    pub fn warnings_mut(&mut self) -> &mut Warnings {
+        match self {
+            EitherManifest::Real(r) => r.warnings_mut(),
+            EitherManifest::Virtual(v) => v.warnings_mut(),
+        }
+    }
     pub(crate) fn workspace_config(&self) -> &WorkspaceConfig {
         match *self {
             EitherManifest::Real(ref r) => r.workspace_config(),

src/cargo/ops/cargo_package.rs

@@ -458,13 +458,17 @@ fn build_lock(ws: &Workspace<'_>, orig_pkg: &Package) -> CargoResult<String> {
     let toml_manifest =
         prepare_for_publish(orig_pkg.manifest().resolved_toml(), ws, orig_pkg.root())?;
     let source_id = orig_pkg.package_id().source_id();
+    let mut warnings = Default::default();
+    let mut errors = Default::default();
     let manifest = to_real_manifest(
         contents.to_owned(),
         document.clone(),
         toml_manifest,
         source_id,
         orig_pkg.manifest_path(),
         gctx,
+        &mut warnings,
+        &mut errors,
     )?;
     let new_pkg = Package::new(manifest, orig_pkg.manifest_path());