Add builtin_functions from gles 2.0 CTS

(Code is licensed under apache 2.0, https://github.com/KhronosGroup/VK-GL-CTS/blob/main/LICENSE so I also added copy of license.)

Probably mainly useful for drivers not natively implementing some instructions.

Edit: I caught regression on r300 with this, so some cases aren't covered yet by shader-db.