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

[via cfe-commits]

================
@@ -307,6 +311,58 @@ After:
       ~pre_foo_post();
     };
 
+.. option:: ClassConstexprCase
+
+    When defined, the check will ensure class constexpr names conform to the
+    selected casing.
----------------
EugeneZelenko wrote:

```suggestion
    When defined, the check will ensure class ``constexpr`` names conform to
    the selected casing.
```

Same in other places.

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