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.