StringAlgorithms: Refactor `cmTokenize()` function

- Refactor and optimize the loop to make it shorter and faster
- Make it push elements into an arbitrary (templated) output iterator
- Make it a template on a separator type with the most used defaults
- Add a backward compatible signature to return `std::vector<std::string>`
- Add an alternative function `cmTokenizedView()` to return a vector of string views