Description:
------------
The order in which an optional parameter is specified should not matter. However, currently, when an optional parameter occurs before a required parameter in a constructor or function argument, the Reflection package is incorrectly identifying the optional parameter as being a required parameter.

Test script:
---------------
<?php
class A {}

class B {
    function __construct($b = null, A $a) {}
}

Reflection::export(new ReflectionClass('B'));

class C {
    function __construct(A $a, $b = null) {}
}

Reflection::export(new ReflectionClass('C'));

https://3v4l.org/gKhZ6
https://3v4l.org/Yt2JN

Expected result:
----------------
Parameter b should be optional regardless of its position in a constructor or function argument.

Actual result:
--------------
Class [ <user> class B ] {
  @@ ./index.php 10-12

  - Constants [0] {
  }

  - Static properties [0] {
  }

  - Static methods [0] {
  }

  - Properties [0] {
  }

  - Methods [1] {
    Method [ <user, ctor> public method __construct ] {
      @@ ./index.php 11 - 11

      - Parameters [2] {
        Parameter #0 [ <required> $b ]
        Parameter #1 [ <required> A $a ]
      }
    }
  }
}

Class [ <user> class C ] {
  @@ ./index.php 16-18

  - Constants [0] {
  }

  - Static properties [0] {
  }

  - Static methods [0] {
  }

  - Properties [0] {
  }

  - Methods [1] {
    Method [ <user, ctor> public method __construct ] {
      @@ ./index.php 17 - 17

      - Parameters [2] {
        Parameter #0 [ <required> A $a ]
        Parameter #1 [ <optional> $b = NULL ]
      }
    }
  }
}