[clang-tidy][NFC] Make CheckFactories::CreateChecks* const

[njames93]

Summary

There's no reason for these methods to be non-const.

clang-tools-extra/clang-tidy/ClangTidyModule.h

template <typename CheckType> void registerCheck(llvm::StringRef CheckName) {
     registerCheckFactory(CheckName,
                          [](llvm::StringRef Name, ClangTidyContext *Context) {
                            return std::make_unique<CheckType>(Name, Context);
                          });
   }
 
   /// Create instances of checks that are enabled.
   std::vector<std::unique_ptr<ClangTidyCheck>>
-  createChecks(ClangTidyContext *Context);
+  createChecks(ClangTidyContext *Context) const;
 
   /// Create instances of checks that are enabled for the current Language.
   std::vector<std::unique_ptr<ClangTidyCheck>>
-  createChecksForLanguage(ClangTidyContext *Context);
+  createChecksForLanguage(ClangTidyContext *Context) const;
 
   typedef llvm::StringMap<CheckFactory> FactoryMap;
   FactoryMap::const_iterator begin() const { return Factories.begin(); }
   FactoryMap::const_iterator end() const { return Factories.end(); }
   bool empty() const { return Factories.empty(); }
 
 private:
   FactoryMap Factories;

clang-tools-extra/clang-tidy/ClangTidyModule.cpp

 namespace tidy {
 
 void ClangTidyCheckFactories::registerCheckFactory(StringRef Name,
                                                    CheckFactory Factory) {
   Factories.insert_or_assign(Name, std::move(Factory));
 }
 
 std::vector<std::unique_ptr<ClangTidyCheck>>
-ClangTidyCheckFactories::createChecks(ClangTidyContext *Context) {
+ClangTidyCheckFactories::createChecks(ClangTidyContext *Context) const {
   std::vector<std::unique_ptr<ClangTidyCheck>> Checks;
   for (const auto &Factory : Factories) {
     if (Context->isCheckEnabled(Factory.getKey()))
       Checks.emplace_back(Factory.getValue()(Factory.getKey(), Context));
   }
   return Checks;
 }
 
 std::vector<std::unique_ptr<ClangTidyCheck>>
-ClangTidyCheckFactories::createChecksForLanguage(ClangTidyContext *Context) {
+ClangTidyCheckFactories::createChecksForLanguage(
+    ClangTidyContext *Context) const {
   std::vector<std::unique_ptr<ClangTidyCheck>> Checks;
   const LangOptions &LO = Context->getLangOpts();
   for (const auto &Factory : Factories) {
     if (!Context->isCheckEnabled(Factory.getKey()))
       continue;
     std::unique_ptr<ClangTidyCheck> Check =
         Factory.getValue()(Factory.getKey(), Context);
     if (Check->isLanguageVersionSupported(LO))