SqlParallel - Implement BatchQueueInterface

SqlParallel - Implement BatchQueueInterface

Before
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Each of the `CRM_Queue_Queue_*` drivers supports a set of methods for
claiming/releasing one queue-item at a time (eg `claimItem()`,
`releaseItem()`, `deleteItem()`).

After
-----

All drivers still support the same queue-item methods.  Additionally, the
`SqlParallel` driver supports batch-oriented equivalents (`claimItems()`,
`deleteItems()`, etc).

Comments
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I initially looked at updating all of the drivers to support queues.  There
were a few obstacles.  Firstly, batched-claims seem semantically
questionable for queues that run 1-by-1 (`Sql`, `Memory`).  Secondly, there
are a few extensions in contrib that extend these classes and override
methods (consequently, they're looking for stable signatures).

The approach here seemed to resolve those two concerns in an OOP-safe way:
define an optional interface (`BatchQueueInterface`) which can be used to
mark enhanced functionality on queues where it makes sense (eg
`SqlParallel`).