Core/Analytics: Make MakeUniqueId() a const member function

This function doesn't modify instance state, so we can mark it as const.

Source/Core/Core/Analytics.cpp

@@ -101,7 +101,7 @@ void DolphinAnalytics::GenerateNewIdentity()
   SConfig::GetInstance().SaveSettings();
 }
 
-std::string DolphinAnalytics::MakeUniqueId(std::string_view data)
+std::string DolphinAnalytics::MakeUniqueId(std::string_view data) const
 {
   std::array<u8, 20> digest;
   const auto input = std::string{m_unique_id}.append(data);

Source/Core/Core/Analytics.h

@@ -89,7 +89,7 @@ private:
   // Returns a unique ID derived on the global unique ID, hashed with some
   // report-specific data. This avoid correlation between different types of
   // events.
-  std::string MakeUniqueId(std::string_view data);
+  std::string MakeUniqueId(std::string_view data) const;
 
   // Unique ID. This should never leave the application. Only used derived
   // values created by MakeUniqueId.