R1:152ddf57092e

Use unicode mode when tokenizing strings like user realnames

Summary:
Fixes T9732. We currently tokenize strings (like user realnames) in the default non-unicode mode, which can cause patterns like `\s` to work incorrectly.

Use `/u` to use unicode-aware tokenization instead.

Test Plan:
The behavior of "\s" depends upon environmental settings like LC_ALL.

With LC_ALL set to "C", `\xA0` is not considered a whitespace character.
With LC_ALL set to "en_US", it is:

```
$ php -r 'setlocale(LC_ALL, "C")…