Surround phone numbers with LTR unicode mark.

This also removes the previous TextView LTR flag that I had initially added for a one-off.

core-util/src/main/java/org/signal/core/util/StringUtil.java

@@ -322,4 +322,8 @@ public final class StringUtil {
     iterator.setText(text);
     return iterator.countBreaks();
   }
+
+  public static String forceLtr(@NonNull CharSequence text) {
+    return "\u202a" + text + "\u202c";
+  }
 }