Add shape inference for SparseLengthsSumSparseLookup
Summary: Just copy whatever corresponding input shape info. Or we will miss the shape info of output of SparseLengthsSumSparseLookup, which will be infered as the input of downstream SparseLengthsSum op, whose int64/int32 mode is undetermined.
Test Plan:
```
buck test caffe2/caffe2/opt:bound_shape_inference_test
```
Reviewed By: khabinov, ChunliF
Differential Revision: D26769226
fbshipit-source-id: 4032bc4643a125095a48fa8c23ca4ebcf26dc29c
