tr: prevent passing options in the wrong place

Note: This requires using the DEPRECATED item Command::trailing_var_arg
in clap. This is going to be another
[problem with clap](https://github.com/tertsdiepraam/uutils-args/blob/main/docs/design/problems_with_clap.md).

src/uu/tr/src/tr.rs

@@ -164,6 +164,7 @@ pub fn uu_app() -> Command {
         .about(ABOUT)
         .override_usage(format_usage(USAGE))
         .infer_long_args(true)
+        .trailing_var_arg(true)
         .arg(
             Arg::new(options::COMPLEMENT)
                 .visible_short_alias('C')

tests/by-util/test_tr.rs

@@ -78,6 +78,14 @@ fn test_complement1() {
         .stdout_is("aX");
 }
 
+#[test]
+fn test_complement_afterwards_is_not_flag() {
+    new_ucmd!()
+        .args(&["a", "X", "-c"])
+        .fails()
+        .stderr_contains("extra operand '-c'");
+}
+
 #[test]
 fn test_complement2() {
     new_ucmd!()
@@ -127,6 +135,22 @@ fn test_complement_multi_early() {
         .stdout_is("aX");
 }
 
+#[test]
+fn test_complement_multi_middle() {
+    new_ucmd!()
+        .args(&["-c", "a", "-c", "X"])
+        .fails()
+        .stderr_contains("tr: extra operand 'X'");
+}
+
+#[test]
+fn test_complement_multi_late() {
+    new_ucmd!()
+        .args(&["-c", "a", "X", "-c"])
+        .fails()
+        .stderr_contains("tr: extra operand '-c'");
+}
+
 #[test]
 fn test_squeeze() {
     new_ucmd!()