[clang-tools-extra] [clang-tidy][NFC] Replace stateless struct with namespace in `readability-identifier-naming` (PR #173506)

[via cfe-commits]

github-actions[bot] wrote:

<!--LLVM CODE LINT COMMENT: clang-tidy-->


:warning: C/C++ code linter, clang-tidy found issues in your code. :warning:

<details>
<summary>
You can test this locally with the following command:
</summary>

```bash

git diff -U0 origin/main...HEAD -- clang-tools-extra/clang-tidy/readability/IdentifierNamingCheck.cpp clang-tools-extra/clang-tidy/readability/IdentifierNamingCheck.h |
python3 clang-tools-extra/clang-tidy/tool/clang-tidy-diff.py   -path build -p1 -quiet
```

</details>

<details>
<summary>
View the output from clang-tidy here.
</summary>

```
clang-tools-extra/clang-tidy/readability/IdentifierNamingCheck.cpp:344:14: error: use of undeclared identifier 'getEnumPrefix' [clang-diagnostic-error]
  344 |     Prefix = getEnumPrefix(ECD);
      |              ^~~~~~~~~~~~~
clang-tools-extra/clang-tidy/readability/IdentifierNamingCheck.cpp:346:14: error: use of undeclared identifier 'getClassPrefix' [clang-diagnostic-error]
  346 |     Prefix = getClassPrefix(CRD, HNOption);
      |              ^~~~~~~~~~~~~~
clang-tools-extra/clang-tidy/readability/IdentifierNamingCheck.cpp:348:34: error: use of undeclared identifier 'getDeclTypeName' [clang-diagnostic-error]
  348 |     const std::string TypeName = getDeclTypeName(ND);
      |                                  ^~~~~~~~~~~~~~~
clang-tools-extra/clang-tidy/readability/IdentifierNamingCheck.cpp:350:16: error: use of undeclared identifier 'getDataTypePrefix' [clang-diagnostic-error]
  350 |       Prefix = getDataTypePrefix(TypeName, ND, HNOption);
      |                ^~~~~~~~~~~~~~~~~
clang-tools-extra/clang-tidy/readability/IdentifierNamingCheck.cpp:421:27: error: use of undeclared identifier 'getAsteriskCount' [clang-diagnostic-error]
  421 |   const size_t PtrCount = getAsteriskCount(ModifiedTypeName);
      |                           ^~~~~~~~~~~~~~~~
clang-tools-extra/clang-tidy/readability/IdentifierNamingCheck.cpp:786:33: error: use of undeclared identifier 'getAsteriskCount'; did you mean 'HungarianNotation::getAsteriskCount'? [clang-diagnostic-error]
  786 |         const size_t PtrCount = getAsteriskCount(Type, ND);
      |                                 ^~~~~~~~~~~~~~~~
      |                                 HungarianNotation::getAsteriskCount
clang-tools-extra/clang-tidy/readability/IdentifierNamingCheck.cpp:525:15: note: 'HungarianNotation::getAsteriskCount' declared here
  525 | static size_t getAsteriskCount(const std::string &TypeName,
      |               ^
clang-tools-extra/clang-tidy/readability/IdentifierNamingCheck.cpp:1382:7: error: no member named 'getDeclTypeName' in namespace 'clang::tidy::readability::HungarianNotation'; did you mean simply 'getDeclTypeName'? [clang-diagnostic-error]
 1382 |       HungarianNotation::getDeclTypeName(Decl), Decl->getName(), Decl, Loc,
      |       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      |       getDeclTypeName
clang-tools-extra/clang-tidy/readability/IdentifierNamingCheck.cpp:707:20: note: 'getDeclTypeName' declared here
  707 | static std::string getDeclTypeName(const NamedDecl *ND) {
      |                    ^
```

</details>


https://github.com/llvm/llvm-project/pull/173506