Convert getSettingsController() to global static object

After looking at the assembly output it became apparent that the Windows
compiler did not compile out the `getSettingsController()` function
call.

This led to an unnecessary function call in order to get the
SettingsController. Turning it into a static object in the compilation
unit scope removes this function call and turns getSettings call into a
single instruction (not counting zeroing the register for comparison and
the jump instruction afterwards).

----

Adding the following code to the `main` function:
```cpp
f ( settings::getSetting( settings::BoolSetting::UTILITY_vrcDebug ) )
{
        LOG( INFO ) << "Enabled";
}
else
{
        LOG( INFO ) << "Disabled";
}
```

Leads to this with the `getSettingsController` function:
```assembly
[...]
    47            if ( settings::getSetting( settings::BoolSetting::UTILITY_vrcDebug ) )
0x7ff6c96819a0  <+ 1024>         call AdvancedSettings!settings::getSettingsController (00007ff6`c96cd280)
0x7ff6c96819a5  <+ 1029>         xorps   xmm0,xmm0
0x7ff6c96819a8  <+ 1032>         cmp     byte ptr [rax+5FCh],0
0x7ff6c96819af  <+ 1039>         je AdvancedSettings!main+0x4fd (00007ff6`c9681a9d)
    49                LOG( INFO ) << "Enabled";
0x7ff6c96819b5  <+ 1045>         mov     qword ptr
[rsp+288h],r15
0x7ff6c96819bd  <+ 1053>         mov     qword ptr
[rsp+290h],rsi
[...]
```

And this without the function:
```assembly
[...]
    47            if ( settings::getSetting( settings::BoolSetting::UTILITY_vrcDebug ) )
0x7ff7d97a19bb  <+ 1019>         xorps   xmm0,xmm0
0x7ff7d97a19be  <+ 1022>         cmp     byte ptr [AdvancedSettings!settings::settingController+0x5fc (00007ff7`d9854d4c)],0
0x7ff7d97a19c5  <+ 1029>         je AdvancedSettings!main+0x4f3 (00007ff7`d97a1ab3)
    49                LOG( INFO ) << "Enabled";
0x7ff7d97a19cb  <+ 1035>         mov     qword ptr
[rsp+288h],r15
0x7ff7d97a19d3  <+ 1043>         mov     qword ptr
[rsp+290h],rsi
[...]
```

Notice the missing `call AdvancedSettings![...]` without the function
and that the settings call literally cannot be made any faster.

src/settings/settings.cpp

@@ -6,63 +6,58 @@
 
 namespace settings
 {
-SettingsController& getSettingsController()
-{
-    static SettingsController s{};
-
-    return s;
-}
+static SettingsController settingController{};
 
 void saveChangedSettings()
 {
-    getSettingsController().saveChangedSettings();
+    settingController.saveChangedSettings();
 }
 
 void saveAllSettings()
 {
     LOG( INFO ) << "Saving all settings.";
-    getSettingsController().saveAllSettings();
+    settingController.saveAllSettings();
     LOG( INFO ) << "All settings saved.";
 }
 
 [[nodiscard]] bool getSetting( const BoolSetting setting )
 {
-    return getSettingsController().getSetting<bool>( setting );
+    return settingController.getSetting<bool>( setting );
 }
 
 void setSetting( const BoolSetting setting, const bool value )
 {
-    getSettingsController().setSetting( setting, value );
+    settingController.setSetting( setting, value );
 }
 
 [[nodiscard]] double getSetting( const DoubleSetting setting )
 {
-    return getSettingsController().getSetting<double>( setting );
+    return settingController.getSetting<double>( setting );
 }
 
 void setSetting( const DoubleSetting setting, const double value )
 {
-    getSettingsController().setSetting( setting, value );
+    settingController.setSetting( setting, value );
 }
 
 [[nodiscard]] int getSetting( const IntSetting setting )
 {
-    return getSettingsController().getSetting<int>( setting );
+    return settingController.getSetting<int>( setting );
 }
 
 void setSetting( const IntSetting setting, const int value )
 {
-    getSettingsController().setSetting( setting, value );
+    settingController.setSetting( setting, value );
 }
 
 [[nodiscard]] std::string getSetting( const StringSetting setting )
 {
-    return getSettingsController().getSetting<std::string>( setting );
+    return settingController.getSetting<std::string>( setting );
 }
 
 void setSetting( const StringSetting setting, const std::string value )
 {
-    getSettingsController().setSetting( setting, value );
+    settingController.setSetting( setting, value );
 }
 
 std::string initializeAndGetSettingsPath()
@@ -70,7 +65,7 @@ std::string initializeAndGetSettingsPath()
     // The static object is initialized the first time the function is called.
     // Having a dedicated function for this allows more control over when this
     // happens.
-    return getSettingsController().getSettingsFileName();
+    return settingController.getSettingsFileName();
 }
 
 } // namespace settings