d3d12: Use compact arrays for clip/cull distance

This puts us more in line with other drivers, and matches what
SPIR-V would produce rather than the GLSL compiler. It also means
we can delete the current fixup pass, since previously clip distance
was always float4s but some components could go unused. Now, clip
distance is an array that's appropriately sized for what's actually
written.

Reviewed-by: Bill Kristiansen <billkris@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9846>

src/gallium/drivers/d3d12/d3d12_screen.cpp

@@ -317,6 +317,9 @@ d3d12_get_param(struct pipe_screen *pscreen, enum pipe_cap param)
    case PIPE_CAP_MAX_VARYINGS:
       return 32;
 
+   case PIPE_CAP_NIR_COMPACT_ARRAYS:
+      return 1;
+
    default:
       return u_pipe_screen_get_param_defaults(pscreen, param);
    }