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

[Valentyn Yukhymenko via cfe-commits]

BaLiKfromUA wrote:

Addressed all comments. Thanks for the initial feedback!

Regarding documentation: looks like we need to merge https://github.com/llvm/llvm-project/pull/122290 first and then update docs in my PR

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