Use sample input for edge ops (#291)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/291

Use sample inputs to generate dtype constraints for edge ops.

This is depending on diff stack D49088856. The purpose of the whole stack is to increase edge ops dtype constraints coverage.

This diff uses the sample input generator DtypeRunner to generate all possible dtype arguments and get back valid ones for each operator.

Reviewed By: manuelcandales

Differential Revision: D49182359

fbshipit-source-id: 7274b56037b53488ad70b28b66a430dcd48754ed