Some engines call setAutosave and some don't. isAutosave is used to
determine if a saved game is an autosave, but in fact, on most cases it
just falls back to comparing the name to "Autosave".
This is wrong for several reasons:
* Older versions of ScummVM used Autosave 0.
* The name "Autosave" is translated, so if you change the language, it
won't be detected.
Instead of relying on the name, use the well-known getAutosaveSlot() from
Engine/MetaEngine.
Fixes#12735.
For each engine:
- Make a new folder detection
- Move detection-related files inside the folder
- Add a new module "enginename/detection"
- Add DETECT_OBJS here
- Adjust the normal engine module to remove detect_objs
- Adjust every file for the new changes.
