P3776 Another motivating example for trailing commas

[fdwr]

Another motivating example we've encountered multiple times in our codebase that's not listed in P3776R1 section 3 is when you later need to add a parameter to an existing function call, but to avoid client breakage, you do so conditionally via the preprocessor and build flags:

    inline Expression Resample(
        Expression input,
        TensorDimensions outputSizes,
        DML_INTERPOLATION_MODE mode,
        DML_AXIS_DIRECTION roundingDirection,
        Span<const float> scales,
        Span<const float> inputPixelOffsets,
        Span<const float> outputPixelOffsets   // <--- want comma here 😀
#if DML_TARGET_VERSION >= 0x6400
        , bool antialiased   // <--- must hackily move it here 🫤
#endif
        )
    {

Because trailing commas are currently prohibited though, you need the ugly hack of moving the last comma in front of the last parameter.