settings: use a template to duplicate memory for each setting

Replaces the type of each variable in the Settings::Values struct with a new
class that allows basic data reading and writing. The new struct
Settings::Setting duplicates the data in memory and can manage global overrides
per each setting.

src/core/hle/kernel/process.cpp

@@ -123,7 +123,7 @@ std::shared_ptr<Process> Process::Create(Core::System& system, std::string name,
                                                               : kernel.CreateNewUserProcessID();
     process->capabilities.InitializeForMetadatalessProcess();
 
-    std::mt19937 rng(Settings::values->rng_seed.value_or(0));
+    std::mt19937 rng(Settings::values->rng_seed.GetValue().value_or(0));
     std::uniform_int_distribution<u64> distribution;
     std::generate(process->random_entropy.begin(), process->random_entropy.end(),
                   [&] { return distribution(rng); });