Update NonZero to slice to number of non-zero elements

[CharlieL7]

Motivation

• NonZero should only output the indices of nonzero values in the input.
• Fixes accuracy of NonZero and makes it consistent with ONNX spec.

Technical Details

• This updates the kernel to output the number of nonzero values and then uses dyn_slice to cut off the padded values.
• Creates a symbolic output shape regardless if the input shape was static.

Changelog Category

Add a CHANGELOG.md entry for any option other than Not Applicable

• • Added: New functionality.
• • Changed: Changes to existing functionality.
• • Removed: Functionality or support that has been removed. (Compared to a previous release)
• • Optimized: Component performance that has been optimized or improved.
• • Resolved Issues: Known issues from a previous version that have been resolved.
• • Not Applicable: This PR is not to be included in the changelog.

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