Foam Web Extension

[riccardoferretti]

This PR is heavily inspired and influenced by #1290 - thanks @pderaaij for spearheading and working through this complex feature. See that PR for more context.

Compared to #1290 , this PR:

• does not introduce webpack, mocha, and double TS settings
• removes (for now) support for testing the web extension (basically, we are still, only, testing the node extension). I know, that's not great, but given the limited testing we were able to do anyways, it feels like a reasonable trade off for the reduced complexity
• avoids some extra dependencies for the migration where possible (e.g. using a sha library that works in both node and browser)

This way:

• we have a working web extension (although a bit brittle as it has no testing of its own - but then again I don't expect many changes that would impact the web extension without affecting the native one)
• we have the code in a place where improvements on this side (including moving to webpack etc) can be done incrementally, as the feature is already there

The only thing I would have liked to add was running a basic test in the web extension (without the need for mocha) that would only test if the extension is present. Then again, this can be added as a second step.

[pderaaij]

Looks good to me!

[riccardoferretti]

Great @pderaaij ! Again, I want to empathise that you basically did all the hard work here, I just repackaged it to avoid those extra dependencies 🙏