Performance update on GenerateQrCode function

[HolyOne]

Faster generation of QRCode using StringBuilder

[gfoidl]

The StringBuilder could be used in GenerateQrCode as well, to avoid the string-manipulations (and these allocations).

[codebude]

Hi @HolyOne , hi @gfoidl Thanks for your support and pointing me onto this topic. I just re-fined your PR a little bit. I think by setting the capacity we can squeeze out even a little bit more performance. 0c54783