tr: implement translate and squeeze (-s) mode

Add translate and squeeze mode to the `tr` program. For example:

    $ printf xx | tr -s x y
    y

Fixes #2141.

tests/by-util/test_tr.rs

@@ -63,6 +63,24 @@ fn test_squeeze_complement() {
         .stdout_is("aaBcDcc");
 }
 
+#[test]
+fn test_translate_and_squeeze() {
+    new_ucmd!()
+        .args(&["-s", "x", "y"])
+        .pipe_in("xx")
+        .run()
+        .stdout_is("y");
+}
+
+#[test]
+fn test_translate_and_squeeze_multiple_lines() {
+    new_ucmd!()
+        .args(&["-s", "x", "y"])
+        .pipe_in("xxaax\nxaaxx")
+        .run()
+        .stdout_is("yaay\nyaay");
+}
+
 #[test]
 fn test_delete_and_squeeze() {
     new_ucmd!()