Skip webextension-polyfill

[fregante]

• Fixes If a tab is closed before the method responds, the Messenger throws "Could not establish connection" #67 (comment)

The polyfill provides little benefit here, especially since we're not dealing with Firefox anymore. Once we switch to MV3 we will be able to drop the polyfill completely, everywhere.

Not yet tested

[fregante]

Context

webextension-polyfill is an abstraction that introduces bugs and limits, while providing little advantage (once MV3 rolls in), for example:

• Closing the receiver tab will not throw an error in tabs.sendMessage() mozilla/webextension-polyfill#365

Status

This PR fixes some issues, but is now abandoned until we're able to use MV3 exclusively.

webextension-polyfill wraps response errors and rejects the promise returned by sendMessage(). Dropping the polyfill at this point means reimplementing this logic on top of webext-polyfill-kinda.

This isn't too difficult, but it's probably not necessary once we can use the natively-promised sendMessage in MV3 — or at the very least it would require further work to adjust it again.

Future

• Drop webext-polyfill-kinda
• Fix remaining broken tests