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.
When doing large string concatenations the default push_back on the
String class can slow down things quite a bit. This is because it
has to constantly reallocate the memory and copy the contents. This
StringBuilder class delays the concatenation until the size of the
resulting string is known.
Rémi Verschelde
Karroffel