Use string views

String views can reduce the amount of copy operations we have to do internally, e.g. for resolving fqons.

For example, string views could be helpful in this situation:

```cpp
member_id = "modpack.path.to.Object";
std::vector<std::string> member_parts = util::split(member_id, '.');
```

The 2nd line could be a vector string views instead of normal strings