Support %P (Password or Secret) in qsprintf()

Summary: Depends on D19781. Fixes T6960. Ref T13217. Ref T13216. Occasionally, we issue queries which contain passwords or secrets. Supporting "%P" (similar to the csprintf() "%P") allows us to mask these in logs and output while still generating the correct values when we actually execute a query.

Test Plan:

$ cat test.php
<?php

require_once 'scripts/init/init-script.php';

$conn = id(new PhabricatorUser())->establishConnection('r');

$query = qsprintf(
  $conn,
  'SELECT %P',
  new PhutilOpaqueEnvelope('hunter2'));

echo $query."\n";
var_dump(queryfx_one($conn, '%Q', $query));

$ php -f test.php
SELECT ********
array(1) {
  ["hunter2"]=>
  string(7) "hunter2"
}

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13217, T13216, T6960

Differential Revision: https://secure.phabricator.com/D19782