A lot of standard functionality can benefit from using abseil

Abseil is a common c++ library that compiles with c++11, but provides features (such as `absl::string_view`) only appeared in c++17. In particular a lot of string copy operations might be a lot cheaper to not copy at all. It also provides flag parsing, has a bunch of container functionality etc.

https://abseil.io/

At this point, it doesn't seem to be commonly packaged yet on various Linuxes, so this would probably have to go into `third_party/`. It's default build system is bazel, but it also can CMake.

(Lower prio for something to consider long-term to avoid having to build a lot of utils. So mostly a strong suggestion at this point)