[desktop] fix audio output engine not saving (#3083)

This issue has like 15 different causes, and I'm surprised it took this
long to pop up.

1. LoadString had a hack *specific* to the AudioEngine enum. Why?
   Solving this was easy, just use the explicit type ctor. -_-
2. The LoadString hack was abused in configure_audio.cpp to get around
   the canonicalization infrastructure that was explicitly put in to
   make this exact operation easier. Why?
3. ToString was also broken because of LoadString's garbage output.
   Technically it might work now, but it's better to just use the
   canonicalization infrastructure that was made specifically for this
   purpose.

Also did a few tiny optimizations in config/settings cuz wynaut.

Signed-off-by: crueter <crueter@eden-emu.dev>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3083
Reviewed-by: Caio Oliveira <caiooliveirafarias0@gmail.com>
Reviewed-by: MaranBr <maranbr@eden-emu.dev>
Reviewed-by: Lizzie <lizzie@eden-emu.dev>

src/common/settings_setting.h

@@ -129,7 +129,7 @@ protected:
         } else if constexpr (std::is_floating_point_v<Type>) {
             return fmt::format("{:f}", value_);
         } else if constexpr (std::is_enum_v<Type>) {
-            return std::to_string(static_cast<u32>(value_));
+            return std::to_string(u32(value_));
         } else {
             return std::to_string(value_);
         }
@@ -192,15 +192,13 @@ public:
             if constexpr (std::is_same_v<Type, std::string>) {
                 this->SetValue(input);
             } else if constexpr (std::is_same_v<Type, std::optional<u32>>) {
-                this->SetValue(static_cast<u32>(std::stoul(input)));
+                this->SetValue(u32(std::stoul(input)));
             } else if constexpr (std::is_same_v<Type, bool>) {
                 this->SetValue(input == "true");
             } else if constexpr (std::is_same_v<Type, float>) {
                 this->SetValue(std::stof(input));
-            } else if constexpr (std::is_same_v<Type, AudioEngine>) {
-                this->SetValue(ToEnum<AudioEngine>(input));
             } else {
-                this->SetValue(static_cast<Type>(std::stoll(input)));
+                this->SetValue(Type(std::stoll(input)));
             }
         } catch (std::invalid_argument&) {
             this->SetValue(this->GetDefault());