fix delegators to allow usage in plugin managers

[stefanotorresi]

see #5172

• move delegator logic from create() to separate method
• remove automatic invokable service for delegator factories
• add delegator factory class validation
• add callback support for delegator factories
• tests

[Ocramius]

While this is indeed clean, consider that I inlined the code for performance reasons

[stefanotorresi]

hmmm but it's 40 lines of code now, plus there are separated methods for each service type. this way it's not only cleaner, it's more consistent too.

are you sure the performance gain is worth it? maybe there is even another way to improve that aspect?

[Ocramius]

Hrm... it's probably ok to keep the method separate then, yep.

[Ocramius]

on add callback support for DelegatorFactories - are you sure you want callback support there?

Should be trivial though:

1. change the check on

   if (!$delegatorFactory instanceof DelegatorFactoryInterface) {

   to

   if (!$delegatorFactory instanceof DelegatorFactoryInterface && !is_callable($delegatorFactory)) {

2. change

   return $delegatorFactory->createDelegatorWithName($serviceManager, $cName, $rName, $creationCallback);

   to

   return $delegatorFactory instanceof DelegatorFactoryInterface 
       ? $delegatorFactory->createDelegatorWithName($serviceManager, $cName, $rName, $creationCallback)
       : $delegatorFactory($serviceManager, $cName, $rName, $creationCallback);

[stefanotorresi]

yep, why not, this way we can keep delegator usage in line with the other service types :)