Add 2d snap transforms option

This is a cut back backport of reduz snapping PR #43194.

It just offers a global project setting for transform snapping.

core/engine.h

@@ -62,6 +62,7 @@ private:
 	int _target_fps;
 	float _time_scale;
 	bool _pixel_snap;
+	bool _snap_2d_transforms;
 	uint64_t _physics_frames;
 	float _physics_interpolation_fraction;
 
@@ -110,6 +111,7 @@ public:
 	Object *get_singleton_object(const String &p_name) const;
 
 	_FORCE_INLINE_ bool get_use_pixel_snap() const { return _pixel_snap; }
+	bool get_snap_2d_transforms() const { return _snap_2d_transforms; }
 
 #ifdef TOOLS_ENABLED
 	_FORCE_INLINE_ void set_editor_hint(bool p_enabled) { editor_hint = p_enabled; }