Added support for firebird 3.x and PHP 8.1

[satwareAG-ironMike]

I've created a fork of 2.7 ( https://github.com/satwareAG/doctrine-firebird-driver/tree/php81-phpunit ) which supports the following:

• doctrine/dbal v2.13.9 with Firebird 3 support
• doctrine/orm: 2.13.4
• PHP 8.1 support with php-firebird 3.0 driver
• sane test environment based on docker php 8.1 dev image with current firebird 3 database for tests
• all tests pass, minor glitch on object destruction
• symfony php unit bridge for easy deprecation hunt

Here's a gist for a quick selftest: https://gist.github.com/satwareAG-ironMike/5cf5396a8f78a40d2bd9484e21973b0e

I'll have to clear some code and then doctrine/dbal 3.5 support is on my list.

@MartinKoeditz I'll need help to figure out the problems with the php-firebird driver tests on php 8.1 mentioned here: https://gist.github.com/satwareAG-ironMike/77ec10f912e3701966dc432913c56561

Everything I did so far was on a current linux distribution using docker so the results may vary.

[satwareAG-ironMike]

We've released Version 3.0.0 of the Doctrine DBAL/ORM Driver.
https://github.com/satwareAG/doctrine-firebird-driver

It is available on Packagist: https://packagist.org/packages/satag/doctrine-firebird-driver

The Driver supports: Firebird 2.5 upto 5.0, PHP 8.1 to 8.3 and dbal ^3.8, support for 4.x is in development.