toco thinks Stack is the same as Pack.

Stack is not Pack.  tf.stack() yields Pack ops. Pack ops stack tensors.  Stack ops manipulate the TF runtime stack.

This cl unaliases "Stack" and "Pack" ops in toco, and renames most things that refer to "Stack" ops to "Pack" to be consistent across the codebase.

In summary:

Stack is whack.  'Stack' should be 'Pack'.  Hack 'Stack's into 'Pack's like a maniac.  This keeps 'Stack's from wracking runtime graphs.

(We apologize for the fault in the change description.  Those responsible have been...er...sacked).

PiperOrigin-RevId: 204951155