[clang-tools-extra] [clang-tidy] Add more constexpr options to `readability-identifier-naming` (PR #162160)

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ChillerDragon wrote:

@HerrCai0907 a constexpr is const so it does not change. A variable means it can vary. Isn't it contradicting then to say a constant variable (`ConstexprVariable`) exists? The way I see it there are constants and there are variables.

https://github.com/llvm/llvm-project/pull/162160