Guardian: Split dashboard and folder guardian implementation (#69722)

* Split dashboard and folder guardian implementations

* Replace guardian constructors

* Simplify tests

* Add tests

* Apply suggestion from code review

Differentiate errors for dashboard and folders

* Remove tests for general folder

* Add tests for general scope

pkg/services/folder/folderimpl/folder.go

@@ -127,7 +127,7 @@ func (s *Service) Get(ctx context.Context, cmd *folder.GetFolderQuery) (*folder.
 	// do not get guardian by the folder ID because it differs from the nested folder ID
 	// and the legacy folder ID has been associated with the permissions:
 	// use the folde UID instead that is the same for both
-	g, err := guardian.NewByUID(ctx, dashFolder.UID, dashFolder.OrgID, cmd.SignedInUser)
+	g, err := guardian.NewByFolder(ctx, dashFolder, dashFolder.OrgID, cmd.SignedInUser)
 	if err != nil {
 		return nil, err
 	}
@@ -204,7 +204,7 @@ func (s *Service) GetChildren(ctx context.Context, cmd *folder.GetChildrenQuery)
 			continue
 		}
 
-		g, err := guardian.NewByUID(ctx, f.UID, f.OrgID, cmd.SignedInUser)
+		g, err := guardian.NewByFolder(ctx, dashFolder, dashFolder.OrgID, cmd.SignedInUser)
 		if err != nil {
 			return nil, err
 		}