[frontend] Slow and Turbo modes (#3525)

Closes #3344

Adds slow and turbo modes with configurable speeds that can then be
toggled by the user. Behavior is:
- Standard/slow limit, toggle turbo = turbo
- Turbo limit, toggle turbo = standard
- Standard/turbo limit, toggle slow = slow
- Slow limit, toggle slow = standard

Enabling the turbo/slow mode enables the frame limiter unconditionally.

This has some conflicts with VSync. For example when I set my refresh
rate to 60hz and enable vsync, turbo mode does nothing. Not sure how to
go about fixing this, @MaranBr probably knows better the proper
solution.

Signed-off-by: crueter <crueter@eden-emu.dev>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3525
Reviewed-by: DraVee <dravee@eden-emu.dev>
Reviewed-by: CamilleLaVey <camillelavey99@gmail.com>

src/common/settings_enums.h

@@ -157,6 +157,7 @@ ENUM(TemperatureUnits, Celsius, Fahrenheit)
 ENUM(ExtendedDynamicState, Disabled, EDS1, EDS2, EDS3);
 ENUM(GpuLogLevel, Off, Errors, Standard, Verbose, All)
 ENUM(GameListMode, TreeView, GridView);
+ENUM(SpeedMode, Standard, Turbo, Slow);
 
 template <typename Type>
 inline std::string_view CanonicalizeEnum(Type id) {