Refactor Git Attribute & performance optimization (#34154)

This PR moved git attributes related code to `modules/git/attribute` sub
package and moved language stats related code to
`modules/git/languagestats` sub package to make it easier to maintain.

And it also introduced a performance improvement which use the `git
check-attr --source` which can be run in a bare git repository so that
we don't need to create a git index file. The new parameter need a git
version >= 2.40 . If git version less than 2.40, it will fall back to
previous implementation.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: yp05327 <576951401@qq.com>

services/repository/files/content.go

@@ -277,28 +277,3 @@ func GetBlobBySHA(ctx context.Context, repo *repo_model.Repository, gitRepo *git
 		Content:  content,
 	}, nil
 }
-
-// TryGetContentLanguage tries to get the (linguist) language of the file content
-func TryGetContentLanguage(gitRepo *git.Repository, commitID, treePath string) (string, error) {
-	indexFilename, worktree, deleteTemporaryFile, err := gitRepo.ReadTreeToTemporaryIndex(commitID)
-	if err != nil {
-		return "", err
-	}
-
-	defer deleteTemporaryFile()
-
-	filename2attribute2info, err := gitRepo.CheckAttribute(git.CheckAttributeOpts{
-		CachedOnly: true,
-		Attributes: []string{git.AttributeLinguistLanguage, git.AttributeGitlabLanguage},
-		Filenames:  []string{treePath},
-		IndexFile:  indexFilename,
-		WorkTree:   worktree,
-	})
-	if err != nil {
-		return "", err
-	}
-
-	language := git.TryReadLanguageAttribute(filename2attribute2info[treePath])
-
-	return language.Value(), nil
-}