Cause <a rel="noopener" target="_top"> navigations to create a new browsing context

[mystor]

Currently the rel="noopener" keyword indicates that new browsing contexts which result from following the hyperlink will not have an opener browsing context, however, if the navigation would normally preserve the browsing context, nothing changes.

It would be nice to be able to get a new independent browsing context without leaving the current browser window, by allowing to cause a new browsing context to be created, simply re-using the browsing window.

[annevk]

How would this affect going backwards in history?

@mikewest

[annevk]

See also #1440 for related discussion on this idea. You effectively need to tie browsing context names to history somehow.

cc @freesamael @johnwilander

[annevk]

This will be simpleish to add once #3740 is a thing and seems desirable.