Use SDL's keyboard grab support now that it's been upstreamed

app/backend/systemproperties.cpp

@@ -68,6 +68,12 @@ SystemProperties::SystemProperties()
     hasDiscordIntegration = false;
 #endif
 
+#ifdef Q_OS_DARWIN
+    supportsWindowedSystemKeyCapture = false;
+#else
+    supportsWindowedSystemKeyCapture = true;
+#endif
+
     unmappedGamepads = SdlInputHandler::getUnmappedGamepads();
 
     // Populate data that requires talking to SDL. We do it all in one shot