* `_gui_input`, `_input`, `_unhandled_input` and `_unhandled_key_input` are now regular C++ virutal functions.
* Everything else converted to GDVIRTUAL
* BIND_VMETHOD is gone, always use the new syntax from now on.
Creating `_gui_input` method and using the binder to register events will no longer work, simply override the virtual function now.
* Added a new macro SNAME() that constructs and caches a local stringname.
* Subsequent usages use the cached version.
* Since these use a global static variable, a second refcounter of static usages need to be kept for cleanup time.
* Replaced all theme usages by this new macro.
* Replace all signal emission usages by this new macro.
* Replace all call_deferred usages by this new macro.
This is part of ongoing work to optimize GUI and the editor.
- Move most properties from TileMap to TileSet,
- Make TileSet more flexible, supporting more feature (several
collision layers, etc...),
- Fusion both the TileMap and TileSet editor,
- Implement TileSetSources, and thus a new way to index tiles in the TileSet,
- Rework the TileSet and TileMap editors completely,
- Implement an editor zoom widget (and use it in several places)
