overlay: option to force software renderer in configurator (#721)

## Link to GitHub Issue or related Pull Request, if one exists
chicken bit for #720

src/spice2x/cfg/configurator.cpp

@@ -9,6 +9,7 @@ namespace cfg {
 
     // globals
     bool CONFIGURATOR_STANDALONE = false;
+    bool CONFIGURATOR_FORCE_SOFTWARE_RENDER = false;
     ConfigType CONFIGURATOR_TYPE = ConfigType::Config;
 
     Configurator::Configurator() {
@@ -26,6 +27,10 @@ namespace cfg {
     // that environments without D3D9 (Wine without dxvk, headless test boxes,
     // GPUs whose drivers reject HAL) still get a working configurator.
     static bool try_init_d3d9(ConfiguratorWindow &wnd) {
+        if (cfg::CONFIGURATOR_FORCE_SOFTWARE_RENDER) {
+            return false;
+        }
+
         if (wnd.hWnd == nullptr) {
             return false;
         }

src/spice2x/cfg/configurator.h

@@ -11,6 +11,7 @@ namespace cfg {
     // globals
     extern bool CONFIGURATOR_STANDALONE;
     extern ConfigType CONFIGURATOR_TYPE;
+    extern bool CONFIGURATOR_FORCE_SOFTWARE_RENDER;
 
     class Configurator {
     private:

src/spice2x/launcher/launcher.cpp

@@ -1358,6 +1358,10 @@ int main_implementation(int argc, char *argv[]) {
         timeutils::TIMER_HACKS_DISABLE = true;
     }
 
+    if (options[launcher::Options::CfgForceSoftwareRender].value_bool()) {
+        cfg::CONFIGURATOR_FORCE_SOFTWARE_RENDER = true;
+    }
+
     // API debugging
     if (api_debug && !cfg::CONFIGURATOR_STANDALONE) {
         API_CONTROLLER = std::make_unique<api::Controller>(api_port, api_pass, api_pretty);

src/spice2x/launcher/options.cpp

@@ -2927,6 +2927,15 @@ static const std::vector<OptionDefinition> OPTION_DEFINITIONS = {
             {"user", ""},
         },
     },
+    {
+        // CfgForceSoftwareRender
+        .title = "Configurator Force Software Rendering",
+        .name = "forcesoftware",
+        .desc = "Forces the use of software rendering instead of hardware acceleration for "
+            "the configurator.",
+        .type = OptionType::Bool,
+        .category = "Development",
+    },
 };
 
 const std::vector<std::string> &launcher::get_categories(Options::OptionsCategory category) {

src/spice2x/launcher/options.h

@@ -291,6 +291,7 @@ namespace launcher {
             DisableHighResTimer,
             EnableICMPHook,
             AutoElevate,
+            CfgForceSoftwareRender
         };
 
         enum class OptionsCategory {