Component: QR code scanning

[pocmo]

We want to wrap the code needed to do QR code scanning in a component (lib-qr).

We currently have two use cases:

• FxA Authentication
• Fenix URL scanning

Fennec currently uses intents to launch an installed barcode scanner. For security reasons we do not want to do that here.

┆Issue is synchronized with this Jira Task

[pocmo]

For the record: AS + csadilek will work on providing this functionality