[clang-tools-extra] [clang-tidy] Add detection of decltype(nullptr) => std::nullptr_t to modernize-use-nullptr (PR #224591)

[Yanzuo Liu via cfe-commits]

================
@@ -51,6 +61,16 @@ Options
    ``NULL``. By default this check will only replace the ``NULL`` macro and will
    skip any similar user-defined macros.
 
+.. option:: useNullptrt
----------------
zwuis wrote:

```suggestion
.. option:: UseNullptrT
```


https://github.com/llvm/llvm-project/pull/224591