Fully roll out sandboxing for all platforms

[digitarald]

Over the past iterations we validated that Electron's sandbox is stable and fast using a staged rollout thanks to many improvements. We are confident enough to roll it out to 100% of users (this iteration) and making it the default (next iteration).

cc @bpasero @deepak1556

[digitarald]

Rollout is at 100% 🎉

[bpasero]

Love the fast turnaround here ;)