Make JavaScript programmatic link clicks open in a new tab and leave Via

When a user clicks on a link in Via it opens the link target in a new tab that is _not_ proxied by Via: https://github.com/hypothesis/viahtml/pull/9

But when the navigation is triggered by programmatically clicking the link using JavaScript this still navigates the original tab and does not leave Via. For example Google and Bing search results do this kind of navigation.

We need to intercept these programmatic link navigations and make them open in a new, non-proxied tab like normal link navigations do.

A one-line JavaScript solution that works for Google and Bing was given in this Slack thread: https://hypothes-is.slack.com/archives/C1M8NH76X/p1621418996025700

Master issue for all kinds of JavaScript navigations: https://github.com/hypothesis/viahtml/issues/183