[feature request] Add masking type for QR codes

[Rampagy]

Thanks for creating such a great app!

I was curious if it would be possible display the mask for QR codes.

I did a little searching and it appears there are 8 possible masks to a QR code:

The library ZXing C++ has to be able to decipher this mask in order to read the QR code. I guess it's a question of whether or not it provides the mask.

These are the 3 bits that encode the mask:

This video from Veritasium describes it really well. https://youtu.be/w5ebcowAJD8?&t=1612

In this example I believe the mask would be 4 (0b100)

I did some quick searching and this was the closest I could find, but unfortunately it only returns if it's a valid mask, but not actually the mask. The maskIndex referenced in that function would be it. https://github.com/zxing-cpp/zxing-cpp/blob/master/core/src/qrcode/QRDataMask.h#L23-L43