Fix webview communication for Safari

[jonah-iden]

What it does

This fixes outgoing messages from webviews being forwarded correctly to theia in safari.
while comparing a ProxyWindow with a Window object works in Firefox and Chrome In Safari they are never equal. Therefore this is now comparing the origin which since webviews are unique should be ok

How to test

Best way is probably through notebook outputs.

Start Theia in any browser you like, create a new notebook and add a simple print('abc') cell. Execute it (you need the jupyter and python extension for this). The output should appear.

Follow-ups

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[jonah-iden]

@jbicker added you since your on mac and can therefore confirm this works correctly in safari

[msujew]

Works well for me on FireFox/Chrome/Electron. I'll give a final approval after someone has tested this on Safari (MacOS).

[msujew]

Alright, approved 👍