[web][native] add white frame around QR code

Summary:
ENG-9875.

Native
before:

after:

Web
before:

after:

Test Plan:
On Android physical device:

1. Scanning QR code when using Add from Linked devices works
2. Scanning QR code using an app camera (deep linking) works

Reviewers: angelika, tomek

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D14055