This change adds `cmake-format` as. a pre-commit hook. The style file closely matches that in Clio, and they will be made to be equivalent over time. For now, some files have been excluded, as those need some manual adjustments, which will be done in future changes.
This change removes unused definitions from the CMake files, moves variable definitions from `XrplSanity` to `XrplSettings` where they better belong, and updates the minimum GCC and Clang versions to match what we actually minimally support.
