Make `TensorFlowFloatingPoint` refine `ElementaryFunctions`. (#217)
Make `TensorFlowFloatingPoint` refine `ElementaryFunctions`. (#217)

Enables use of `ElementaryFunctions` requirements on
`TensorFlowFloatingPoint`-constrained types, e.g.
`T.log(2)` where `T: TensorFlowFloatingPoint`.
tensorflow/swift-apis,tensorflow/swift-apis,tensorflow/swift-apis,tensorflow/swift-apis,tensorflow/swift-apis