* Add merge_rank function

* Update infer_windowed_reduction_output_shape to use PartialShape

* Minor simplification

* Some unit tests and (whaddaya know) fixes for infer_windowed_reduction_output_shape

* Update infer_batched_pooling_forward to use PartialShape

* Update pooling fprop ops for partial shapes

* Update pooling bprop ops for partial shapes

* Add test-failing reminders to implement unit tests for partial shape/type prop for pooling ops

* Add unit tests for partial shape propagation for poolign ops

* Nuke C-style casts for Dimensions/Ranks in validation_util.cpp