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

[Baranov Victor via cfe-commits]

vbvictor wrote:

> GlobalConstexprVariableCase because there's already ConstexprVariableCase

I'm +1 on `GlobalConstexprVariableCase` to keep consistent, plus I don't see why `constexpr` declarations can't be variables. `constexpr` variable can be calculated at compile time by `constexpr`/`constinit` functions, so It doesn't have to hold some predefined literal value.

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