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
As pointed out in https://reviews.llvm.org/D119130#3829816, this
introduces a clang AST dependency to the clangToolingInclusions, which is used
by clang-format.
Since rest of the inclusion tooling doesn't depend on clang ast, moving this
into a separate library.
Differential Revision: https://reviews.llvm.org/D135245