Add QR scanner

[silvaDominic]

Checklist

• I made sure that there are no existing issues - open or closed - to which I could contribute my information.
• I made sure that there are no existing discussions - open or closed - to which I could contribute my information.
• I have read the FAQs inside the app (Menu -> About -> FAQs) and my problem isn't listed.
• I have taken the time to fill in all the required details. I understand that the bug report will be dismissed otherwise.
• This issue contains only one feature request.
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Feature description

The camera app should incorporate a QR scan feature.

Why do you want this feature?

Every commercial camera app features a QR scan feature. Even GrapheneOS's stock camera features one. Given how prevalent QR codes are today, this app, while intended to be simple, still feels to be missing a standard camera feature.

How this should be implemented is subject to discussion. Most commercial ones autodetect. GrapheneOS's has a dedicated camera mode. I'd personally opt for whatever is simplest to implement.

Additional information

No response

[Aga-C]

It's a duplicate of #25.