overlay: re-enable keyboard navigation (#802)

## Link to GitHub Issue or related Pull Request, if one exists
Fixes #800 

## Description of change
Restores keyboard navigation by default in spicecfg, and add an option
to optionally enable it in the overlay.

## Testing

src/spice2x/launcher/launcher.cpp

@@ -1115,6 +1115,9 @@ int main_implementation(int argc, char *argv[]) {
     if (options[launcher::Options::DisableOverlay].value_bool()) {
         overlay::ENABLED = false;
     }
+    if (options[launcher::Options::OverlayKeyboardNavigation].value_bool()) {
+        overlay::ENABLE_KEYBOARD_NAVIGATION = true;
+    }
     if (options[launcher::Options::OverlayScaling].is_active() && !cfg::CONFIGURATOR_STANDALONE && !cfg_run) {
         const auto val = options[launcher::Options::OverlayScaling].value_uint32();
         if (10 <= val && val <= 400 && val != 100) {

src/spice2x/launcher/options.cpp

@@ -510,6 +510,13 @@ static const std::vector<OptionDefinition> OPTION_DEFINITIONS = {
         .type = OptionType::Bool,
         .category = "General Overlay",
     },
+    {
+        .title = "Overlay Keyboard Navigation",
+        .name = "keyboardnav",
+        .desc = "Enables keyboard navigation in the in-game overlay.",
+        .type = OptionType::Bool,
+        .category = "General Overlay",
+    },
     {
         // OverlayScaling
         .title = "Spice Overlay UI Scale %",

src/spice2x/launcher/options.h

@@ -53,6 +53,7 @@ namespace launcher {
             SOFTID,
             VREnable,
             DisableOverlay,
+            OverlayKeyboardNavigation,
             OverlayScaling,
             NotificationPosition,
             spice2x_FpsAutoShow,