This patch mechanically replaces None with std::nullopt where the
compiler would warn if None were deprecated. The intent is to reduce
the amount of manual work required in migrating from Optional to
std::optional.
This is part of an effort to migrate from llvm::Optional to
std::optional:
https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716
The plan is to use this to use this for .clang-format, .clang-tidy, and
compile_commands.json. (Currently the former two are reparsed every
time, and the latter is cached forever and changes are never seen).
Differential Revision: https://reviews.llvm.org/D88172
