Reproduce unexpected MySQL warnings for binary values

The prepared statement emulation layer is handling binary content in a
way that creates warnings in MySQL.

When analysing the query logs, we saw that the content sent to the
server is missing `0x5C` characters when the using emulated prepares.

This introduces a minimal test case that reproduces the issue to aid the
solution.

More info: doctrine/dbal#6522 (comment)

Signed-off-by: Luís Cobucci <lcobucci@gmail.com>

Author: lcobucci

ext/pdo_mysql/tests/pdo_mysql_prepare_emulated_binary.phpt

@@ -0,0 +1,44 @@
+--TEST--
+MySQL PDO->prepare(), no warnings should be raised for binary values using emulated PS
+--EXTENSIONS--
+pdo_mysql
+--SKIPIF--
+<?php
+require_once __DIR__ . '/inc/mysql_pdo_test.inc';
+MySQLPDOTest::skip();
+?>
+--FILE--
+<?php
+    require_once __DIR__ . '/inc/mysql_pdo_test.inc';
+    $db = MySQLPDOTest::factory();
+    $db->setAttribute(PDO::ATTR_EMULATE_PREPARES, true);
+
+    $content = '0191D886E6DC73E7AF1FEE7F99EC6235';
+
+    $statement = $db->prepare('SELECT HEX(?) as test');
+    $statement->bindValue(1, hex2bin($content), PDO::PARAM_LOB);
+    $statement->execute();
+
+    var_dump($statement->fetchAll(PDO::FETCH_ASSOC)[0]['test'] === $content);
+    var_dump($db->query('SHOW WARNINGS')->fetchAll(PDO::FETCH_ASSOC));
+
+    $db->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
+
+    $statement2 = $db->prepare('SELECT HEX(?) as test');
+    $statement2->bindValue(1, hex2bin($content), PDO::PARAM_LOB);
+    $statement2->execute();
+
+    var_dump($statement2->fetchAll(PDO::FETCH_ASSOC)[0]['test'] === $content);
+
+    $db->setAttribute(PDO::ATTR_EMULATE_PREPARES, true); // SHOW WARNINGS can only be used when PDO::ATTR_EMULATE_PREPARES=true
+    var_dump($db->query('SHOW WARNINGS')->fetchAll(PDO::FETCH_ASSOC));
+    print "done!";
+?>
+--EXPECTF--
+bool(true)
+array(0) {
+}
+bool(true)
+array(0) {
+}
+done!