Lower required GL version to 3.3 + extension

Закрыто xottab-duty запросил слияние github/fork/375gnu/gl33-test в xd_dev

Created by: 375gnu

just an experiment. instead of GL_ARB_gpu_shader5 GL_ARB_texture_gather must be used as in https://github.com/dolphin-emu/dolphin/pull/1259/files.

potentially it's possible, so if there is an interest i can complete this pr