onnxruntime

[Android NNAPI EP] Add support for dynamic output (#4650)

* add dynamic output shape support

* fix bugs associates with scalar inputs

* addressed comments, fixed issue the output buffer size is not correctly set, refactor shaper class

* split the execution logic from nnapi::Model into nnapi::Execution

* update comments for certain scenarios, 1. dynamic output buffer size, 2. ONNX scalar input

* move ctor of nnapi::Execution to public