Account for QR code where embedded text is long

As of #746, we show text below the draft testing QR code, where the text is embedded in the image. For #666, we plan to add text below the app user QR code (the project name and/or the app user name).

We don't currently wrap the text below the QR code, which means that it has the potential to become long. For #666, we'll probably need to figure out some way to wrap the text. Maybe we could use `Intl.Segmenter` to break up the text into words. Once we have text wrapping in place for #666, I think we should probably apply it to the draft testing QR code. "Temporary Testing Code" isn't the shortest string in English, so I assume it will be even longer in other locales.

I'm filing this issue in part because I think we should remember to check on the text below the draft testing QR code once translations have come in for that text. Because of how we float the image in the component, if the text below the QR code becomes too long, it will crowd out the explanatory text on the right.