(explicit) kernel methods in TensorFlow.

## Bug Fixes and Other Changes

*   In python, `Operation.get_attr` on type attributes returns the Python DType
    version of the type to match expected get_attr documentation rather than the
    protobuf enum.
*   tensorflow/contrib/rnn undergoes RNN cell variable renaming for consistency

    MutableOperandRange getArgOperandsMutable() {
      return getArgsMutable();
    }

    // Returns the callee of this operation.
    CallInterfaceCallable getCallableForCallee() { return getFAttr(); }
    // Sets the callee from the callable.
    void setCalleeFromCallable(CallInterfaceCallable callee);

    // returns the callee of this operation.
    func::FuncOp func() {