Add specification for SegmentMax-16

[p-wysocki]

Details:

• Specification for tf.math.segment_max (https://www.tensorflow.org/api_docs/python/tf/math/segment_max)

Tickets:

• CVS-158914

[rkazants]

Let us have EmbeddingSegmentsMax similar to EmbeddingSegmentsSum.
It should also have default index (defining default value for empty segment)

[rkazants]

we should have default value for empty segments, otherwise, we will have additional computation graph (that is not trivial) to compute empty segments and replace zero value

[p-wysocki]

The default value seems to be 0, according to https://www.tensorflow.org/api_docs/python/tf/raw_ops/SegmentMax. I don't think we should expand the op on our own, especially since we only expect it to come from TF FE.

[rkazants]

please define input shapes and output shape for each input and describe what dimensions are equal

[p-wysocki]

data can have any rank and dimensions, so it's described as ND of any numerical type. segment_ids are specified to be a 1D tensor of non-negative, sorted integer numbers of size equal to the size of the first dimension of the input tensor.

Could you please specify what's missing? I think the shapes are covered, but I may be missing something.

[p-wysocki]

Let us have EmbeddingSegmentsMax similar to EmbeddingSegmentsSum.

EmbeddingSegmentX is for sparse inputs, while SegmentMax I'm implementing (to unlock some models) accepts dense inputs, so I don't think it should be added as EmbeddingSegmentMax. I'm moving the discussion to internal channels, if it results in changes, I'll apply them to the PR.