When running on the Steam Deck, launcher mode is now handled

Steamworks recommends not using launchers on the Deck, but it has a
special mode that specifically enables a KB/M layout to assist - we now
enable that before launching the game.

launcher/core/include/steamapi.h

@@ -4,5 +4,9 @@ class LauncherCore;
 
 class SteamAPI {
 public:
-    SteamAPI(LauncherCore& core);
+    explicit SteamAPI(LauncherCore& core);
+
+    void setLauncherMode(bool isLauncher);
+
+    bool isDeck() const;
 };

launcher/core/src/launchercore.cpp

@@ -58,6 +58,8 @@ void LauncherCore::buildRequest(const ProfileSettings& settings, QNetworkRequest
 }
 
 void LauncherCore::launchGame(const ProfileSettings& profile, const LoginAuth& auth) {
+    steamApi->setLauncherMode(false);
+
 #ifdef ENABLE_WATCHDOG
     if (profile.enableWatchdog) {
         watchdog->launchGame(profile, auth);
@@ -486,6 +488,8 @@ LauncherCore::LauncherCore(bool isSteam)
 #endif
 
     readInitialInformation();
+
+    steamApi->setLauncherMode(true);
 }
 
 ProfileSettings& LauncherCore::getProfile(int index) {

launcher/core/src/steamapi.cpp

@@ -17,4 +17,18 @@ SteamAPI::SteamAPI(LauncherCore& core) {
             qDebug() << "Failed to initialize steam api!";
     }
 #endif
-}
+}
+
+void SteamAPI::setLauncherMode(bool isLauncher) {
+#ifdef ENABLE_STEAM
+    SteamUtils()->SetGameLauncherMode(isLauncher);
+#endif
+}
+
+bool SteamAPI::isDeck() const {
+#ifdef ENABLE_STEAM
+    return SteamUtils()->IsSteamRunningOnSteamDeck();
+#else
+    return false;
+#endif
+}