* [phi] move sequence_pool kernel to phi

* mv kernels impl

* fix parameter error

* clean include

* fix compat filename

* [phi] move fluid sequence_pool_grad to phi

* [phi][compat] sig rm GradVarName

* [phi] fix sequence_pool out type

* [phi] rm impl, add const string

* [phi] fix const str

* fix sequence_pooling cmake

* [phi] mv sequence_pooling_test

* [phi] fix grad sig

* [phi] fix sequence_pool is_test error

* [phi] fix sequence_pooling gpu include

* [phi] mv to impl

* [phi] fix SequencePoolFunctor cu include

* [phi] modify out max_index int32_t

* [phi] add pooltype mapping determine

* [phi] fix sequence_pool_sig

* [phi] fix sequence_pool_sig sum

* [phi] try ci

* [phi] fix max_index optional