[API 2.0] Add transformer apis#26418

Merged

guoshengCS merged 22 commits intoPaddlePaddle:developfrom

guoshengCS:add-api-transformer

Aug 24, 2020

Commits on Aug 15, 2020

Add MultiHeadAttention api.
guoshengCS
committed

Commits on Aug 17, 2020

Add MultiHeadAttention cache type and gen_cache.
guoshengCS
committed

Commits on Aug 18, 2020

Commits on Aug 20, 2020

Commits on Aug 23, 2020

Update Transformer apis by renaming MultiheadAttention and cal_kv according to comments.
guoshengCS
committed
Fix MultiHeadAttention in test_transformer_api.py.
guoshengCS
committed