Avoid creating unnecessary temporary cat file sub process (#33942)

Extract from #33934 

In the same goroutine, we should reuse the exist cat file sub process
which exist in `git.Repository` to avoid creating a unnecessary
temporary subprocess.

This PR reuse the exist cate file writer and reader in
`getCommitFromBatchReader`.
It also move `prepareLatestCommitInfo` before creating dataRc which will
hold the writer so other git operation will create a temporary cat file
subprocess.

modules/git/tag.go

@@ -21,11 +21,6 @@ type Tag struct {
 	Signature *CommitSignature
 }
 
-// Commit return the commit of the tag reference
-func (tag *Tag) Commit(gitRepo *Repository) (*Commit, error) {
-	return gitRepo.getCommit(tag.Object)
-}
-
 func parsePayloadSignature(data []byte, messageStart int) (payload, msg, sign string) {
 	pos := messageStart
 	signStart, signEnd := -1, -1