Fix c# generated string marshalling

[arsher]

I hope this is the last one, same as previous fix just for the string bits that I missed.

[ralfbiedert]

Thanks!

[ralfbiedert]

Quick update, I changed array handling in that it now really only allows for the exact number of elements and throws otherwise. I'd argue that's the only correct thing to do:

Like, this works:

    [Theory]
    [InlineData(new byte[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 })]
    public void array_1(byte[] array)
    {
        Assert.Equal((array?.Length ?? 0) > 0 ? 1 : 0, Interop.array_1(new Array
        {
            data = array
        }));
    }

And these won't work:

    [Theory]
    [InlineData(new byte[] { })]
    [InlineData(new byte[] { 1, 2, 3 })]
    [InlineData(new byte[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 })]
    [InlineData(null)]
    public void array_1_throws(byte[] array)
    {
        Assert.Throws<System.InvalidOperationException>(() =>  Interop.array_1(new Array
        {
            data = array
        }));
    }

Does that make sense?