Factor timestep calculation out to Game function

This is so we can grab the game's timestep anywhere else in the codebase
without copy-pasting it.

desktop_version/src/Game.cpp

@@ -6742,3 +6742,33 @@ void Game::copyndmresults(void)
     ndmresulthardestroom = hardestroom;
     SDL_memcpy(ndmresultcrewstats, crewstats, sizeof(ndmresultcrewstats));
 }
+
+static inline int get_framerate(const int slowdown)
+{
+    switch (slowdown)
+    {
+    case 30:
+        return 34;
+    case 24:
+        return 41;
+    case 18:
+        return 55;
+    case 12:
+        return 83;
+    }
+
+    return 34;
+}
+
+int Game::get_timestep(void)
+{
+    switch (gamestate)
+    {
+    case EDITORMODE:
+        return 24;
+    case GAMEMODE:
+        return get_framerate(slowdown);
+    default:
+        return 34;
+    }
+}

desktop_version/src/Game.h

@@ -292,6 +292,7 @@ public:
     bool  colourblindmode;
     bool noflashingmode;
     int slowdown;
+    int get_timestep(void);
 
     bool nodeathmode;
     int gameoverdelay;

desktop_version/src/main.cpp

@@ -57,23 +57,6 @@ static volatile Uint32 accumulator = 0;
 static volatile Uint32 f_time = 0;
 static volatile Uint32 f_timePrev = 0;
 
-static inline Uint32 get_framerate(const int slowdown)
-{
-    switch (slowdown)
-    {
-    case 30:
-        return 34;
-    case 24:
-        return 41;
-    case 18:
-        return 55;
-    case 12:
-        return 83;
-    }
-
-    return 34;
-}
-
 enum FuncType
 {
     Func_null,
@@ -665,19 +648,7 @@ static void inline deltaloop(void)
     const float rawdeltatime = static_cast<float>(time_ - timePrev);
     accumulator += rawdeltatime;
 
-    Uint32 timesteplimit;
-    if (game.gamestate == EDITORMODE)
-    {
-        timesteplimit = 24;
-    }
-    else if (game.gamestate == GAMEMODE)
-    {
-        timesteplimit = get_framerate(game.slowdown);
-    }
-    else
-    {
-        timesteplimit = 34;
-    }
+    Uint32 timesteplimit = game.get_timestep();
 
     while (accumulator >= timesteplimit)
     {