Add methods on TransferManager which transfer to/from device memory specified...

Add methods on TransferManager which transfer to/from device memory specified by ShapedBuffer rather than DeviceMemoryBase. This is part of a broader replacement of DeviceMemoryBase->ShapedBuffer in several XLA interfaces. With this change TransferManager no longer has to allocate memory to transfer tuples to the device. The existing methods using DeviceMemoryBase will be removed in a followup cl.

Various related changes:

* Make the transfer_manager_test an xla_test so that it runs on all the platforms.

* Make several of the TransferManager methods protected.

* Change ScopedShapedBuffer::Allocate to only allocate device memory buffers, and not fill in the tuple index table. The index table is filled in by the transfer manager. This is a cleaner separation of concerns.

PiperOrigin-RevId: 176015628