Add LpPool-18 - add ceil_mode and dilations attributes

[p-wysocki]

Signed-off-by: p-wysocki przemyslaw.wysocki@intel.com

Description

Add LpPool-18, which now has ceil_mode and dilations attributes. Deprecate auto_pad, like it is done in the case of AveragePool and MaxPool.

Motivation and Context

• Partially solves Inconsistencies between MaxPool, AveragePool, and LpPool specs #2290, but more discussion may be needed.

Notes

• LpPoolOpSchemaGenerator uses convPoolShapeInference, which already accounts for ceil_mode attribute. As far as I understand, it makes adding the attribute to ceil_mode trivial, as it is done in this PR. The same goes for the dilations attribute.
• The tests for LpPool are non-existent (there is not such a file as onnx/onnx/backend/test/case/node/lppool.py). Is it intentional? Pooling operators seem to have a lot of common code, so maybe LpPool is considered to be covered by tests for MaxPool and AveragePool. I am not sure if it is intended or an overlook.
• The issue touches on the subject of alignment of Pooling operators. Their attributes are as follows:
  
  A related PR concerns removing storage_order attribute from the MaxPool operator: Add MaxPool-18 - remove storage_order attribute #4533.

[kraiskil]

I don't see why explicit LpPool tests would be left out intentionally. After all, the differnt pools calculate different things.

In my experience, when writing a backend, such coverage tests are very valuable, partly as a safety net but also as additional documentation / clarification. I can not see any big cost in adding such tests, except of course for the initial effort of writing them.

[gramalingam]

Agree with @kraiskil ... adding the test-cases would be useful.

[gramalingam]

Why not add the dilations attribute as well?

[p-wysocki]

@kraiskil @gramalingam I'm working on both adding tests and adding dilations attribute.