iidx, sdvx: booting fullscreen with three or more monitors (#612)

## Link to GitHub Issue or related Pull Request, if one exists
#345 

Hoping that #180 is also addressed by this change, but I can't test it.

## Description of change

IIDX (TDJ) and SDVX (Valk) will now be able to boot in full screen even
with 3 or more monitors attached.

spice will "hide" from the game any monitors other than the primary
monitor and one other monitor for subscreen, allowing it to boot without
crashing - accomplished by clearing `DISPLAY_DEVICE_ATTACHED_TO_DESKTOP`
flag when monitors are enumerated over `EnumDisplayDevicesA`, and
fortunately both games seem to respect that flag.

Add options (one for IIDX, another for SDVX) that lets you specify the
monitor ID of the second monitor.

When the option is set, user-specified monitor will be used as the
subscreen. When the option is not set, spice will just pick the
lowest-indexed monitor as the subscreen, not counting the primary one of
course.

## Testing
Tested both games with three monitors. Should probably work for four or
more.

src/spice2x/launcher/options.cpp

@@ -928,6 +928,17 @@ static const std::vector<OptionDefinition> OPTION_DEFINITIONS = {
             {"bottomright", "for landscape"},
         },
     },
+    {
+        // SDVXSubMonitorOverride
+        .title = "SDVX Subscreen Monitor Override",
+        .name = "sdvxsubmonitor",
+        .desc = "If you have three or more monitors, this option can be set to tell the game which monitor is the subscreen.",
+        .type = OptionType::Text,
+        .setting_name = "\\\\.\\DISPLAY3",
+        .game_name = "Sound Voltex",
+        .category = "Monitor",
+        .picker = OptionPickerType::Monitor,
+    },
     {
         .title = "Force Load DDR Module",
         .name = "ddr",
@@ -2343,6 +2354,17 @@ static const std::vector<OptionDefinition> OPTION_DEFINITIONS = {
         .game_name = "Beatmania IIDX",
         .category = "Game Options",
     },
+    {
+        // IIDXSubMonitorOverride
+        .title = "IIDX TDJ Subscreen Monitor Override",
+        .name = "iidxsubmonitor",
+        .desc = "If you have three or more monitors, this option can be set to tell the game which monitor is the subscreen.",
+        .type = OptionType::Text,
+        .setting_name = "\\\\.\\DISPLAY3",
+        .game_name = "Beatmania IIDX",
+        .category = "Monitor",
+        .picker = OptionPickerType::Monitor,
+    },
     {
         // spice2x_IIDXEmulateSubscreenKeypadTouch
         .title = "IIDX TDJ Subscreen Keypad Touch Emulation",