Add shortName in nsIURI

In legacy/trac#28005 (moved), we integrated the https-everywhere aliasing system for (securedrop) onion addresses. I think we can simplify the patch (and future patches) by including the alias/name within the current browser instance uri (browser.currentURI). We can achieve this by adding a shortName attribute (or something similar) in netwerk/base/nsIURI.idl. For simplicity, host can remain as the onion address, and we can add an additional attribute for the human-meaningful name.

(Naming is hard, but luckily this is an implementation detail so it doesn't really matter which attribute label we choose)

This will simplify patches where, in the current situation, we must pass around both the current uri and onionAliasURI.