Display human-readable text instead of cryptic filemodes (#26352)

Now, you don't need to be a git expert anymore to know what these
numbers mean.

## Before

![grafik](9a964bf6-10fd-40a6-aeb2-ac8f437f8c32)

## After

![grafik](84573cb9-55b6-4dde-9866-95f71b657554)

or when the mode actually changed:

![grafik](0f327538-ebdc-40e7-8c99-f9e21b67f638)

services/gitdiff/gitdiff.go

@@ -427,6 +427,23 @@ func (diffFile *DiffFile) ShouldBeHidden() bool {
 	return diffFile.IsGenerated || diffFile.IsViewed
 }
 
+func (diffFile *DiffFile) ModeTranslationKey(mode string) string {
+	switch mode {
+	case "040000":
+		return "git.filemode.directory"
+	case "100644":
+		return "git.filemode.normal_file"
+	case "100755":
+		return "git.filemode.executable_file"
+	case "120000":
+		return "git.filemode.symbolic_link"
+	case "160000":
+		return "git.filemode.submodule"
+	default:
+		return mode
+	}
+}
+
 func getCommitFileLineCount(commit *git.Commit, filePath string) int {
 	blob, err := commit.GetBlobByPath(filePath)
 	if err != nil {