Feature request: allow camera zoom when scanning QRCode

When scanning Jade's QR Code with an old android phone, sometimes it's difficult to scan the QR code because it can be small, blurred and with incorrect exposure.

Putting the phone closer to the QR code can only make it blurrier. So users with older phones have to find perfect lighting condition and the right Jade/phone distance to get a focused image.

IMO it would be nice to:
- be able to zoom-in during the QR scanning (just like we can do with the regular phone camera).
- the above should help focusing AND having a better image exposure, which should make QR codes easier to scan.

I have also seen users think they need to match the border of the QR code with the frame of the QR overlay:

I think not having the overlay would be less confusing.

BlueWallet already works like the suggestion of this PR. Would be great to have it on Blockstream Green as well.