[clang-tools-extra] [clang-tidy][NFC] Enable `bugprone-unchecked-optional-access` in `clang-tidy` config and fix warnings (PR #170004)

[via cfe-commits]

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zeyi2 wrote:

This modification causes 5 cases to fail:
```
  Clang Tools :: clang-tidy/checkers/bugprone/dynamic-static-initializers.hpp
  Clang Tools :: clang-tidy/checkers/bugprone/suspicious-include.cpp
  Clang Tools :: clang-tidy/checkers/misc/use-anonymous-namespace.cpp
  Clang Tools :: clang-tidy/checkers/misc/use-internal-linkage-func.cpp
  Extra Tools Unit Tests :: clang-tidy/./ClangTidyTests/LLVMHeaderGuardCheckTest/FixHeaderGuards
```

I suspect that there may be some lifetime issues (and also the use of `std::vector/string`, will try to fix them soon)

https://github.com/llvm/llvm-project/pull/170004