[lldb][NFCI] Change return type of Properties::GetExperimentalSettingsName

[bulbazord]

Summary

Most users of this stick it into a StringRef. The one user that doesn't
just tries to get the length out of it, which we can precompute by
putting it in a constexpr StringLiteral.

[jingham]

LGTM

lldb/include/lldb/Core/UserSettingsController.h

public:
 
   // We sometimes need to introduce a setting to enable experimental features,
   // but then we don't want the setting for these to cause errors when the
   // setting goes away.  Add a sub-topic of the settings using this
   // experimental name, and two things will happen.  One is that settings that
   // don't find the name will not be treated as errors.  Also, if you decide to
   // keep the settings just move them into the containing properties, and we
   // will auto-forward the experimental settings to the real one.
-  static const char *GetExperimentalSettingsName();
+  static llvm::StringRef GetExperimentalSettingsName();
 
   static bool IsSettingExperimental(llvm::StringRef setting);
 
   template <typename T>
   T GetPropertyAtIndexAs(uint32_t idx, T default_value,
                          const ExecutionContext *exe_ctx = nullptr) const {
     return m_collection_sp->GetPropertyAtIndexAs<T>(idx, exe_ctx)
         .value_or(default_value);

lldb/source/Core/UserSettingsController.cpp

 Properties::GetSubProperty(const ExecutionContext *exe_ctx,
                            ConstString name) {
   OptionValuePropertiesSP properties_sp(GetValueProperties());
   if (properties_sp)
     return properties_sp->GetSubProperty(exe_ctx, name);
   return lldb::OptionValuePropertiesSP();
 }
 
-const char *Properties::GetExperimentalSettingsName() { return "experimental"; }
+llvm::StringRef Properties::GetExperimentalSettingsName() {
+  static constexpr llvm::StringLiteral g_experimental("experimental");
+  return g_experimental;
+}
 
 bool Properties::IsSettingExperimental(llvm::StringRef setting) {
   if (setting.empty())
     return false;
 
   llvm::StringRef experimental = GetExperimentalSettingsName();
   size_t dot_pos = setting.find_first_of('.');
   return setting.take_front(dot_pos) == experimental;
 }

lldb/source/Interpreter/OptionValueProperties.cpp

OptionValueProperties::GetSubValue(const ExecutionContext *exe_ctx,
 
   switch (sub_name[0]) {
   case '.': {
     lldb::OptionValueSP return_val_sp;
     return_val_sp =
         value_sp->GetSubValue(exe_ctx, sub_name.drop_front(), error);
     if (!return_val_sp) {
       if (Properties::IsSettingExperimental(sub_name.drop_front())) {
-        size_t experimental_len =
-            strlen(Properties::GetExperimentalSettingsName());
+        const size_t experimental_len =
+            Properties::GetExperimentalSettingsName().size();
         if (sub_name[experimental_len + 1] == '.')
           return_val_sp = value_sp->GetSubValue(
               exe_ctx, sub_name.drop_front(experimental_len + 2), error);
         // It isn't an error if an experimental setting is not present.
         if (!return_val_sp)
           error.Clear();
       }
     }