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/diff.go

@@ -65,7 +65,7 @@ func getRepoRawDiffForFileCmd(ctx context.Context, repo *Repository, startCommit
 		files = append(files, file)
 	}
 
-	cmd := gitcmd.NewCommand().WithDir(repo.Path)
+	cmd := gitcmd.NewCommand().WithRepo(repo)
 	switch diffType {
 	case RawDiffNormal:
 		if len(startCommit) != 0 {
@@ -310,7 +310,7 @@ func GetAffectedFiles(ctx context.Context, repo *Repository, branchName, oldComm
 	cmd := gitcmd.NewCommand("diff", "--name-only").AddDynamicArguments(oldCommitID, newCommitID)
 	stdoutReader, stdoutReaderClose := cmd.MakeStdoutPipe()
 	defer stdoutReaderClose()
-	err := cmd.WithEnv(env).WithDir(repo.Path).
+	err := cmd.WithEnv(env).WithRepo(repo).
 		WithPipelineFunc(func(ctx gitcmd.Context) error {
 			// Now scan the output from the command
 			scanner := bufio.NewScanner(stdoutReader)