Images: add mirror extension type

This adds a new mirror image extension type for shaders and
geometry nodes (next to the existing repeat, extend and clip
options).

See D16432 for a more detailed explanation of `wrap_mirror`.

This also adds a new sampler flag `GPU_SAMPLER_MIRROR_REPEAT`.
It acts as a modifier to `GPU_SAMPLER_REPEAT`, so any `REPEAT`
flag must be set for the `MIRROR` flag to have an effect.

Differential Revision: https://developer.blender.org/D16432

intern/cycles/device/cuda/device_impl.cpp

@@ -952,6 +952,9 @@ void CUDADevice::tex_alloc(device_texture &mem)
     case EXTENSION_CLIP:
       address_mode = CU_TR_ADDRESS_MODE_BORDER;
       break;
+    case EXTENSION_MIRROR:
+      address_mode = CU_TR_ADDRESS_MODE_MIRROR;
+      break;
     default:
       assert(0);
       break;