[WIP]Add beam search feature in transformer model (#2834)
[WIP]Add beam search feature in transformer model (#2834)

* add beam search feature

* Update beam search feature and unit test

* add symbolToLogits function set check

* update clearState and add serial test

* add SequenceBeamSearch to python layers

* add createSequenceBeamSearch method to python api
intel-analytics/BigDL,yangw1234/BigDL,yangw1234/BigDL,intel-analytics/BigDL,yangw1234/BigDL,yangw1234/BigDL,intel-analytics/BigDL,intel-analytics/BigDL