Add HQx and xBR shaders

### Description

This PR adds a new upscaling shader called [HQx](https://github.com/Armada651/hqx-shader) which is a very efficient shader with low system requirements. This shader will replace the old xBR shader as the preferred upscaling shader for low-end systems.

This PR also updates the xBR shader with its much improved multipass variants. The system requirements for this shader are now significantly higher. In return it should achieve a level of quality on par or even better than SABR at a lower cost in resources due to its multi-pass implementation.

This PR also adds support for LUT textures as it is required for HQx support.

### To-Do
- [ ] Find out why the workaround in 5a84764 is necessary and fix it.