Given how nsIPrintSettings is passed around, stored and copied all over the
place, it's very hard to reason about where and when a RemotePrintJobChild is
needed or valid. This patch avoids all that by explicitly passing a
RemotePrintJobChild when it's needed.
Another reason to make this change is because RemotePrintJobChild really does
not belong on nsIPrintSettings. That interface is supposed to represent a
collection of settings for laying out the document that is to be printed.
Differential Revision: https://phabricator.services.mozilla.com/D146380
e5a8eb1650