testing/php7-pecl-decimal: upgrade to 2.0.0

Ref https://pecl.php.net/package-info.php?package=decimal&version=2.0.0

PS: tests fails a lot so added patchs

• https://github.com/php-decimal/ext-decimal/commit/d983b8f76f59996339a434c40d1f57703fadbd42
• https://github.com/php-decimal/ext-decimal/commit/da58684a3c95fb52263a85523be9fdab98697503
• https://github.com/php-decimal/ext-decimal/commit/e71f1488b666e30e4f0121a10fee3eeab22bd327