Make QR code exportable as image

[SelinaBuff]

Discussed in #3870

^{Originally posted by Resaki1 February 15, 2024}
Currently, the QR code to share a session is rendered as an SVG. Right-clicking it does not give the option to save the QR code as an image (at least in Chromium). Of course you could make a screenshot, but rendering it as an image would make it easier imo

[Schwehn42]

using canvas instead of svg and upscaling it does the trick