[clang-tools-extra] [clang-tidy][readability-identifier-length] refactoring and cleanup (PR #194610)

[Alex Dutka via cfe-commits]

================
@@ -32,19 +32,19 @@ class IdentifierLengthCheck : public ClangTidyCheck {
   const unsigned MinimumExceptionNameLength;
   const unsigned MinimumParameterNameLength;
 
-  std::string IgnoredVariableNamesInput;
+  llvm::StringRef IgnoredVariableNamesInput;
----------------
dutkalex wrote:

Should I also change `llvm::Regex` to just `Regex` also then?

https://github.com/llvm/llvm-project/pull/194610