[clang] [clang-tidy] [dataflow] Cache reference accessors for `bugprone-unchecked-optional-access` (PR #128437)

[Valentyn Yukhymenko via cfe-commits]

BaLiKfromUA wrote:

TODO: update release notes and `clang-tools-extra/docs/clang-tidy/checks/bugprone/unchecked-optional-access.rst` if needed

https://github.com/llvm/llvm-project/pull/128437