Sparse fill empty rows op

[codeislife99]

This PR is to support SparseFillEmptyRows Op (similar to https://www.tensorflow.org/api_docs/python/tf/sparse/fill_empty_rows) in relay. Frontend code for the TF Op will be added in a following PR since it combines multiple ops together)

[codeislife99]

cc : @trevor-m @comaniac @zhiics PTAL

[comaniac]

@tkonolige @mbrookhart PTAL and approve or request changes explicitly. Thanks.

[tkonolige]

I've suggested some more small changes.

Given the discussion with @mbrookhart, I think you should use dynamic shape here.

[tkonolige]

@comaniac Every time I select request changes on GitHub, it switches it "suggested changes". Maybe because I am not a committer?

[comaniac]

@comaniac Every time I select request changes on GitHub, it switches it "suggested changes". Maybe because I am not a committer?

Yes that's the case, but we'll do our best to make sure all comments are addressed before merging.

[mbrookhart]

I don't fully understand the point of these sparse op PRs, is there a particular model we're trying to target? It's hard for me to review without understanding the use case.

There are issues in this set of PRs that will prevent them from working on dynamically shaped input tensors. I don't think that's a blocker, but it could cause headaches down the road.

[codeislife99]

@tkonolige @mbrookhart This PR is ready for re-review as well whenever you are back from vacation.

[codeislife99]

Hoping back onto this stream of work after a while, was involved with something else.
Since this PR had a lot of issues, it has been completely rewritten in #7442 and addresses all the existing comments in this PR. This Op has also been tested E2E with the customer model. Please review #7442.