[clang] [C++26] [Contracts] Support Parser, AST and AST Serialization (1/n) (PR #205739)

[Peter Bindels via cfe-commits]

dascandy wrote:

WRT Eric's branch, I've worked with Eric to test changes he made and to test it (see also the issues on his fork), and right now it ICEs on one contract assertion in my (private) code base. GCC 16.1 also ICEs on one, but a different one. As such, from a user point of view it's very close to the same quality level as GCC, and redoing that work seems counterproductive unless there's a different reason to do so.

https://github.com/llvm/llvm-project/pull/205739