Bind an already-compiled event handler function to a name in the given scope object. The same restrictions on aName (lowercase ASCII, not too long) applies here as for CompileEventHandler. Scripting languages with static scoping must re-bind the scope chain for aHandler to begin (after the activation scope for aHandler itself, typically) with aTarget's scope.
Logically, this 'bind' operation is more of a 'copy' - it simply stashes/associates the event handler function with the event target, so it can be fetched later with GetBoundEventHandler().
Referenced by nsScriptEventHandlerOwnerTearoff::CompileEventHandler().