Use Utf8NoBom instance in more places

[Kermalis]

With the latest commit 0595c9c, Utf8StringToNative.Utf8NoBom was introduced for safety. However, there are other places in the library where Encoding.UTF8 is still used. For example, GameRichPresenceJoinRequested_t

internal string ConnectUTF8() => System.Text.Encoding.UTF8.GetString( Connect, 0, System.Array.IndexOf<byte>( Connect, 0 ) );

The generator should be updated to use the new NoBom instance.