graphics: option to include subscreens in screenshot (#866)

## Link to GitHub Issue or related Pull Request, if one exists
#0

## Description of change
Adds `-screenshotsub`. Off by default. When on, screenshots include the
subscreens. All subscreens are captured, even if they are hidden from
view. Works for all four screens of gitadora arena model as well.

This should also fix an issue with API / companion app not capturing
gitadora subscreen correctly.

Note: only done for DX9... DX11 will need another PR to make this work.

Unrelated to this PR, there seems to be a bug with gitadora not
accepting mouse or api touch input.

## Testing

src/spice2x/hooks/graphics/graphics.cpp

@@ -119,6 +119,7 @@ uint32_t GRAPHICS_FS_ORIGINAL_HEIGHT = 0;
 std::string GRAPHICS_DEVICEID = "PCI\\VEN_1002&DEV_7146";
 std::string GRAPHICS_SCREENSHOT_DIR = ".\\screenshots";
 bool GRAPHICS_SCREENSHOT_INCLUDE_OVERLAY = false;
+bool GRAPHICS_SCREENSHOT_SUBSCREENS = false;
 
 static decltype(ChangeDisplaySettingsA) *ChangeDisplaySettingsA_orig = nullptr;
 static decltype(ChangeDisplaySettingsExA) *ChangeDisplaySettingsExA_orig = nullptr;
@@ -1531,7 +1532,7 @@ bool graphics_capture_receive_jpeg(int screen, TooJpeg::WRITE_ONE_BYTE receiver,
     return success;
 }
 
-std::string graphics_screenshot_genpath() {
+std::string graphics_screenshot_genpath(const std::vector<int> &screens) {
 
     // verify dir path
     if (GRAPHICS_SCREENSHOT_DIR.empty()) {
@@ -1556,11 +1557,21 @@ std::string graphics_screenshot_genpath() {
     auto tm_now = *std::gmtime(&t_now);
     auto prefix = to_string(std::put_time(&tm_now, "%Y%m%d"));
 
-    // find next filename
+    // find next filename; the whole set has to be free so one shot stays numbered together
     size_t id = 0;
     while (true) {
         auto filepath = fmt::format("{}\\{}_{}.png", GRAPHICS_SCREENSHOT_DIR, prefix, id);
-        if (!fileutils::file_exists(filepath)) {
+        bool available = !fileutils::file_exists(filepath);
+        for (const auto screen : screens) {
+            if (!available) {
+                break;
+            }
+            if (screen != 0) {
+                available = !fileutils::file_exists(fmt::format(
+                        "{}\\{}_{}_{}.png", GRAPHICS_SCREENSHOT_DIR, prefix, id, screen));
+            }
+        }
+        if (available) {
             return filepath;
         }