Now that we have a compilation phase for the DIC, using tags after compilation
is not needed anymore.
Tags were introduced to allow several independant bundles to be able to
interact which each others (remember that each extension knows nothing about
the others).
But during the compilation phase, the container has been merged ans so, all
the information from all bundles are available. This is then the right place
to deal with tags. That way, less work is needed at runtime and the DIC class
in the cache is also much smaller.
For simple cases, it means that you need to process the tag in a compiler pass
and store the information you need in a DIC parameter (have a look at the
TranslatorPass for a very simple example).
So, the PHP dumper does not add tags to the dumped PHP class anymore (it does
not implements TaggedContainerInterface anymore). But tags are still available
on ContainerBuilder instances.
