fix(gitdiff): unquote C-quoted paths from git diff-tree --raw (#39781)

`parseGitDiffTreeLine` (`services/gitdiff/git_diff_tree.go`) read
`BasePath`/`HeadPath` straight from `git diff-tree --raw` output without
undoing git's C-quoting, unlike its sibling `parseLsTreeLine`
(`modules/git/parse.go`), which already does this with
`strconv.Unquote`.

This fix applies the same unquoting to both paths in the diff-tree
parser.

---------

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

modules/git/parse.go

@@ -56,13 +56,17 @@ func parseLsTreeLine(line []byte) (*LsTreeEntry, error) {
 		return nil, fmt.Errorf("invalid ls-tree output (invalid object id): %q, err: %w", line, err)
 	}
 
-	if len(entryName) > 0 && entryName[0] == '"' {
-		entry.Name, err = strconv.Unquote(string(entryName))
-		if err != nil {
-			return nil, fmt.Errorf("invalid ls-tree output (invalid name): %q, err: %w", line, err)
-		}
-	} else {
-		entry.Name = string(entryName)
+	entry.Name, err = UnquoteDiffFilePath(string(entryName))
+	if err != nil {
+		return nil, fmt.Errorf("invalid ls-tree output (invalid name): %q, err: %w", line, err)
 	}
 	return entry, nil
 }
+
+func UnquoteDiffFilePath(path string) (string, error) {
+	// ref: see the document of git config's "core.quotepath"
+	if !strings.HasPrefix(path, `"`) {
+		return path, nil
+	}
+	return strconv.Unquote(path)
+}