Migrate scanner flow to zxing-cpp with CameraX

[nielstron]

This migrates the scanner away from zxing (which is barely maintained) to zxing-cpp. A neat side effect is that the scanning is much faster and catches more difficult/blurred/smaller/etc pictures.

[SeineEloquenz]

This is interesting. I don't know the zxing-cpp lib, but if this can also write codes the same way as the other zxing lib did, maybe we could get rid of that one completely.

[nielstron]

Unfortunately it looks like zxing-cpp does not support code generation

[nielstron]

The only reasonable alternative to zxing for generation I see so far is https://github.com/woo-j/OkapiBarcode which at least had updates as recently as two weeks ago and seems to support a decent amount of configurable settings, and would avoid all the baggage from zxing for scanning/views that we don't need.

[nielstron]

I explored how difficult it would be to migrate to okapi and seems not very hard. One qualm I have is that I don't know how many issues like #491 or #184 will appear. We don't really have a test suite for this yet I guess?

[SeineEloquenz]

No we don't. The problem is that most of the passes I could use for testing contain potentially PII so I can't upload to GitHub. If I anonymize the data, I don't know whether they would still be representative. We had issues like #184 where newer zxing versions render codes that are technically correct, but some scanners don't implement the necessary functionality (ECI), so round trip tests would not help either. I guess we would have to check in the actual expected bitmatrices to get a reliable suite.

We absolutely need a test suite to prevent such regressions before I am willing to change anything related to zxing. But even with the passes I have there is still a lot of risk, because I only got like 20 or so...