Implement BufferHubProducer::attachBuffer

1/ Introduce new kOpProducerQueueInsertBuffer operation to insert a
   standalone ProducerChannel into a ProducerQueueChannel.
2/ Introduce some PDX security check against channel_id spoofing.

Bug: 69981968
Bug: 79224574
Test: buffer_hub_queue-test, libgui_test
Change-Id: I3c13e2897476c34e6e939756b079fe3440937236