Bug 1685454 - [marionette] Enhance retry logic for getMarionetteCommandsActorProxy for inactive actors. r=marionette-reviewers,jdescottes, a=jcristau

When the window of the current child actor instance is moved
into bfcache the actor doesn't get destroyed. Instead
this.contentWindow will become "null", which means that the
command has to be run again in the active actor instance.

By raising a specific error message in the child actor, the
commands actor proxy can handle that error for its retry logic.

Differential Revision: https://phabricator.services.mozilla.com/D101055