c10::string_view (#26616)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/26616
Implement C++17 std::string_view for C++11.
This is useful for compile time type name retrievaly which I'm going to stack on top of this.
It is also useful to replace `const std::string&` with throughout our codebase.
ghstack-source-id: 92100314
Test Plan: unit tests
Differential Revision: D17518992
fbshipit-source-id: 48e31c677d51b0041f4b37e89a92bd176d4a0b08
