[native] Handle invite links in chats

Summary:
Currently, clicking the link results in opening a popup and then a page in Safari. This seems to be a feature of iOS https://linear.app/comm/issue/ENG-4408#comment-a667ee51.

This diff fixes the issue by checking if a link is an invite link and overriding the default behavior. Instead of showing a popup, we're calling the same function that is called when deep links are clicked. But in order to do that we need to replace our handler with a context so that this function becomes accessible outside it.

https://linear.app/comm/issue/ENG-4408/opening-invite-link-from-ios-app-opens-safari

Test Plan:
Send a message with https://comm.app/invite/secret and check if clicking the link results in link modal being shown.
Check if links with other urls, e.g. https://comm.app still work as previously.

Reviewers: kamil, inka

Reviewed By: inka

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D8637