Send Referer header on refresh.
This applies for refreshes resulting from either a <meta> refresh or
the Refresh header. Referrer Policy is honored.
Because exposing the referrer in a new place could have privacy
implications, this behavior is gated behind a disabled pref until
anti-tracking has been considered in bug 1928294.
Some WPTs that D227450 touches are cleaned up a bit.
Differential Revision: https://phabricator.services.mozilla.com/D227450
bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=266554
gecko-commit: 29698232d001764b094d8294c95af2b4dd40419c
gecko-reviewers: peterv, ckerschb, dom-core, smaug