Send requests for .onion domains through Tor even in non-private browsing

[riastradh-brave]

When a user types a .onion domain into the URL bar, the request should be sent through Tor even if not in a private browsing tab, so that onion services just work out of the box.

If/when we add I2P support too, the same mechanism can presumably be used for .i2p domains.

[diracdeltas]

as a first pass, browser-laptop can block the request (before it hits DNS) and show a warning to open the URL in a private tab so it can be resolved

[catilac]

@diracdeltas is there an issue in browser-laptop for this yet?