Add API endpoint to request contents of multiple files simultaniously (#34139)

Adds an API POST endpoint under `/repos/{owner}/{repo}/file-contents`
which receives a list of paths and returns a list of the contents of
these files.

This API endpoint will be helpful for applications like headless CMS
(reference: https://github.com/sveltia/sveltia-cms/issues/198) which
need to retrieve a large number of files by reducing the amount of
needed API calls.

Close #33495

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/git/repo_object.go

@@ -85,17 +85,3 @@ func (repo *Repository) hashObject(reader io.Reader, save bool) (string, error)
 	}
 	return strings.TrimSpace(stdout.String()), nil
 }
-
-// GetRefType gets the type of the ref based on the string
-func (repo *Repository) GetRefType(ref string) ObjectType {
-	if repo.IsTagExist(ref) {
-		return ObjectTag
-	} else if repo.IsBranchExist(ref) {
-		return ObjectBranch
-	} else if repo.IsCommitExist(ref) {
-		return ObjectCommit
-	} else if _, err := repo.GetBlob(ref); err == nil {
-		return ObjectBlob
-	}
-	return ObjectType("invalid")
-}