Emit a stable reference to the interface guid

[AArnott]

This way, the reference can be converted by others into a pointer and passed around without fear that the data will move.

The new property looks like this:

static ref readonly Guid IComIID.Guid
{
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    get
    {
        ReadOnlySpan<byte> data = new byte[] {
            0x0B,0x01,0x00,0x00,0x00,0x00,0x00,0x00,0xC0,0x00,0x00,0x00,0x00,0x00,0x00,0x46 };
        return ref Unsafe.As<byte, Guid>(ref MemoryMarshal.GetReference(data));
    }
}

Also add non-marshaling runtime test project so we can verify the emitted guid has the right value.

[AArnott]

CC: @tannergooding @JeremyKuhne

[JeremyKuhne]

🚀 Nice!

[AArnott]

/azp run

[azure-pipelines]

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