Helper class for XR interfaces that generates VRS images. This class is used by various XR interfaces to generate VRS textures that can be used to speed up rendering. Generates the VRS texture based on a render [param target_size] adjusted by our VRS tile size. For each eyes focal point passed in [param eye_foci] a layer is created. Focal point should be in NDC. The result will be cached, requesting a VRS texture with unchanged parameters and settings will return the cached RID. The minimum radius around the focal point where full quality is guaranteed if VRS is used as a percentage of screen size. The strength used to calculate the VRS density map. The greater this value, the more noticeable VRS is.