[Wilds] Sanitize UTF8 output in tsprintf(...) under Windows

Summary:
Ref T13209. In PHP, when you `echo` or `print` certain invalid sequences to the `cmd.exe` terminal under Windows 10, the entire string just vanishes into the ether.

I ran into this because `arc unit` was reporting "1 failing test" but not actually printing a test failure. That's because the failing test was the surrogate filtering test, and the test failure contained a reserved UTF16 surrogate sequence ("Expected: <filtered result>; Actual: <unfiltered result>"). See D19724.

To try to limit the damage this can cause, explicitly `phutil_utf8ize(...)` the output under Windows. When we don't //need// to do this I think it's slightly better not to (occasionally, the raw input might be useful in debugging or understanding something) which is why I'm not just doing it unconditionally.

Test Plan:
  - Wrote a script which did `echo tsprintf("%s", "<invalid surrogate sequence>");`.
  - On Windows 10 in `cmd.exe`, saw it print something instead of printing nothing.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13209

Differential Revision: https://secure.phabricator.com/D19725

src/xsprintf/PhutilTerminalString.php

@@ -70,6 +70,13 @@ final class PhutilTerminalString extends Phobject {
       $value = preg_replace('/\r(?!\n)/', '<CR>', $value);
     }
 
+    // See T13209. If we print certain invalid unicode byte sequences to the
+    // terminal under "cmd.exe", the entire string is silently dropped. Avoid
+    // printing invalid sequences.
+    if (phutil_is_windows()) {
+      $value = phutil_utf8ize($value);
+    }
+
     return $value;
   }
 }