Only externally visible changes should be a few changed includes as well as
some formatting changes.
PiperOrigin-RevId: 353226662
Change-Id: Iebf5be13774efcbd94c5d5a17b9b27e47275b229
Practically all current compilers fully support C++17 by now, with the exception of `filesystem` (which we won't use).
PiperOrigin-RevId: 281494879
Change-Id: Ia0ef650ede4e5907e4a6421b8ad11743c8bae88f