Update on "refactor cuda_backend.cpp"

This diff does a comprehensive refactor on cuda_backend.cpp. Two main points:
1.  Reuse ExecuTorch standard macros (ET_CHECK_OR_RETURN_ERROR and others) to replaces exiting if..else + ET_LOG branches
2. Introduced LOAD_SYMBOL macro to concentrate the symbol loading pipeline.

Differential Revision: [D84135844](https://our.internmc.facebook.com/intern/diff/D84135844/)

[ghstack-poisoned]

Author: Gasoonjia