Refactor the usage of batch catfile (#31754) (#31889)

Backport #31754 by @lunny

When opening a repository, it will call `ensureValidRepository` and also
`CatFileBatch`. But sometimes these will not be used until repository
closed. So it's a waste of CPU to invoke 3 times git command for every
open repository.

This PR removed all of these from `OpenRepository` but only kept
checking whether the folder exists. When a batch is necessary, the
necessary functions will be invoked.

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

modules/git/tree_nogogit.go

@@ -33,7 +33,10 @@ func (t *Tree) ListEntries() (Entries, error) {
 	}
 
 	if t.repo != nil {
-		wr, rd, cancel := t.repo.CatFileBatch(t.repo.Ctx)
+		wr, rd, cancel, err := t.repo.CatFileBatch(t.repo.Ctx)
+		if err != nil {
+			return nil, err
+		}
 		defer cancel()
 
 		_, _ = wr.Write([]byte(t.ID.String() + "\n"))