Uprade to comlink v4
Created by: felixfbecker
Closes #3989.
There were a bunch or renames, and StringMessageChannelAdapter is no longer bundled with comlink. There is a new experimental string channel support, that is less leaky.
Corresponding upstream comlink PR to fix types: https://github.com/GoogleChromeLabs/comlink/pull/451
Tested manually in the webapp and browser extension.