ggml: add ggml_can_fuse_subgraph (llama/16662)

ggml: add ggml_can_fuse_subgraph (llama/16662)

* ggml: add ggml_can_fuse_subgraph

* ggml-cuda: use ggml_can_fuse_subgraph for topk-moe

* format

* 1. remove inputs from signature as they are transient nodes
2. add check for views: view_src should be part of the subgraph

* - combine check into one loop
- check all view_src parents
- other minor review comments

* remove redudant if test

* - rename and other minor review comments

* add assert about count < 32