Add HasInputs/HasOutputs in shape interface

[Yancey1989]

Maybe we need to add interfaces HasInputs/HasOutputs in InferShapeContextBase

[typhoonzero]

More details please?

Can this be done by

PADDLE_ENFORCE_NOT_NULL(ctx.InputVar("Input"),
                            "some error.");

[Yancey1989]

Maybe there is no InputVar in InferShapeContextBase. After Refactoring InferShape, the inferface name in Infershape context become more clearly, but there is only HasInput/HasOutput to check single Input/Output, so I want to add HasInputs/HasOutputs to check MultiInput/MultiOutput.