Allow centering barcodes when fullscreen

[tjmills-dev]

Related to #2821

At the moment, when using the fullscreen barcode view it hugs the top of the screen (see below). From a UI perspective I do think it looks a bit cramped, but also can present some usage challenges - I have a Pixel 10 which has an in-screen camera, and this interrupts the barcode.

It would be good to get at least some padding, even if user position control is not possible

This behaviour is less of an issue with 2D codes due to the whitespace padding:

[TheLastProject]

Question though: what is the use case of centering the barcode in the full screen mode?

The barcode is already relatively centered in the regular UI. The full screen mode exists to push the barcode to the top of the screen for really cramped spaces (some stores have their barcode scanner placed in a way that fits a small plastic card but not a full phone, so in the regular view the barcode cannot be reached by the scanner because it is too far from the edges).

[tjmills-dev]

I take your point, this might be a somewhat niche improvement. I would add, in addition to phones with cameras in the display, some people might have large cracks or scratches that interfere with the barcode display if it's fixed to the top, so being able to move it might help there.
I suppose it's also possible that in some circumstances the non-fullscreen view might be too small, but that's probably quite a limited issue given you can usually move at least the screen or the scanner closer.