Fix BG tile bug from switching from pink SS

If you had a pink space station background, and switched to a different
tileset, some solid tiles would be placed instead. This commit fixes
that by transforming the room into the basic autotiling tiles before
changing the tileset itself. The reason why I chose this solution is
because it will help with a future change, being unhardcoding warp zone
backgrounds (which'll help with custom autotiling, if that becomes a
thing.)

desktop_version/src/Editor.h

@@ -177,6 +177,8 @@ public:
 
     bool lines_can_pass(int x, int y);
 
+    void make_autotiling_base(void);
+
     int get_enemy_tile(int t);
 
     void switch_tileset(const bool reversed);