Using `misc/scripts/fix_headers.py` on all Godot files.
Some missing header guards were added, and the header inclusion order
was fixed in the Bullet module.
This field represents if the class is exposed to the scripting API.
The value is 'true' if the class was registered manually ('ClassDB::register_*class()'), otherwise it's false (registered on '_post_initialize').
- Added missing registration of classes that are meant to be exposed.