shaders are not updated to be compiled with DXC 1.8

[ASDAlexander77]

shaders are not updated to use DXC 1.8

file MathHelpers.slang line 158: should be

    return float2(
        (1.f - abs(v.x)) * select(v.x >= 0.f, 1.f, -1.f),
        (1.f - abs(v.y)) * select(v.y >= 0.f, 1.f, -1.f));

file GeometryHelpers.slang line 63: should be

    float3 iPos = float3(
        asfloat(asint(pos.x) + select(pos.x < 0.f, -iOff.x, iOff.x)),
        asfloat(asint(pos.y) + select(pos.y < 0.f, -iOff.y, iOff.y)),
        asfloat(asint(pos.z) + select(pos.z < 0.f, -iOff.z, iOff.z))
    );

line 67: should be

    return float3(
        select(abs(pos.x) < origin, pos.x + fOff.x, iPos.x),
        select(abs(pos.y) < origin, pos.y + fOff.y, iPos.y),
        select(abs(pos.z) < origin, pos.z + fOff.z, iPos.z)