refactor: make git package handle all git operations (#38543)

before: gitrepo vs git packages
after: git package fully handle all git operations

by the way, use `WithRepo(repo)` instead of `WithDir(repo.Path)` to hide
path details.

benefits:

1. remove all unnecessary wrappers, developers no need to struggle with
"which package should be used"
2. simplify code, RepositoryFacade can (will) be used everywhere, all
"path" details are (will be) hidden

modules/git/tag.go

@@ -5,6 +5,7 @@ package git
 
 import (
 	"bytes"
+	"context"
 	"sort"
 
 	"gitea.dev/modules/util"
@@ -114,3 +115,8 @@ func sortTagsByTime(tags []*Tag) {
 	sorter := tagSorter(tags)
 	sort.Sort(sorter)
 }
+
+// IsTagExist returns true if given tag exists in the repository.
+func IsTagExist(ctx context.Context, repo RepositoryFacade, name string) bool {
+	return IsReferenceExist(ctx, repo, TagPrefix+name)
+}