gitadora: (arena model) single window mode + subscreen overlay (#486)

## Link to GitHub Issue, if one exists
#477 

## Description of change
This is a work in progress.

What works:
- [x] subscreen overlay shows the touch screen image (in windowed mode)
- [x] touch works in the overlay
- [x] only the main window is shown, other windows are not launched

What doesn't:
- [ ] game occasionally crashes when entering test menu?
- [ ] full screen mode is not tested at all due to monitor requirements
- [ ] need more polish (various options to control the behavior)

src/spice2x/launcher/options.cpp

@@ -978,6 +978,15 @@ static const std::vector<OptionDefinition> OPTION_DEFINITIONS = {
         .category = "Game Options",
         .elements = {{"1", "DX"}, {"2", "SD"}, {"3", "SD2 - white cab"}},
     },
+    {
+        // GitaDoraArenaSingleWindow
+        .title = "GitaDora Arena Single Window (EXPERIMENTAL)",
+        .name = "gdaonewindow",
+        .desc = "For Arena Model, when combined with windowed mode, only show the main game window; enables subscreen overlay",
+        .type = OptionType::Bool,
+        .game_name = "GitaDora",
+        .category = "Game Options",
+    },
     {
         // GitaDoraLefty
         .title = "GitaDora Lefty Guitar (for Digital Wailing)",
@@ -1011,6 +1020,20 @@ static const std::vector<OptionDefinition> OPTION_DEFINITIONS = {
         .game_name = "GitaDora",
         .category = "Game Options",
     },
+    {
+        // GitaDoraSubOverlaySize
+        .title = "GitaDora Subscreen Overlay Size",
+        .name = "gdsubsize",
+        .desc = "Default size of the subscreen overlay. Default: medium",
+        .type = OptionType::Enum,
+        .game_name = "GitaDora",
+        .category = "Overlay",
+        .elements = {
+            {"small", ""},
+            {"medium", ""},
+            {"large", ""}
+        },
+    },
     {
         .title = "Force Load Jubeat Module",
         .name = "jb",