[llvm-branch-commits] [Clang] Move AllocToken frontend options to LangOptions (PR #163635)

[Marco Elver via llvm-branch-commits]

https://github.com/melver created https://github.com/llvm/llvm-project/pull/163635

This change moves the `AllocTokenMax` from `CodeGenOptions` and introduces a
new `AllocTokenMode` to `LangOptions`. Note, `-falloc-token-mode=` deliberately
remains an internal experimental option.

This refactoring is necessary because these options influence frontend
behavior, specifically constexpr evaluation of `__builtin_infer_alloc_token`.
Placing them in `LangOptions` makes them accessible during semantic analysis
frontend, which occurs before codegen.