Support sharing of URLs

[ithinkihaveacat]

Via navigator.share() if available, with fallback to our own UI; see Introducing the Web Share API.

Fallback will probably want to use Cut and Copy commands. (Which possibly works on iOS too.)

[ithinkihaveacat]

(I've applied for an origin trial token.)

[ithinkihaveacat]

Also probably useful: https://github.com/zenorocha/clipboard.js

[samthor]

Unfortunately navigator.share is no longer being offered via Origin Trial, but may get launched properly in the future.

[juliantoledo]

@samthor @ithinkihaveacat Is there any other alternative we could use?

[ithinkihaveacat]

I think the origin trial was the only way to invoke the system share dialog on any platform. Without it, the best we can do is clipboard access.