When adding an Array or Dictionary to itself operator String() got in an
infinite loop. This commit adds a stack to operator String() (Through
the use of a new 'stringify method'). This stack keeps track of all
unique Arrays and Dictionaries it has seen. When a duplicate is found
only a static string is printed '[...]' or '{...}'.
This mirror Python's behavior in a similar case.
This allows more consistency in the manner we include core headers,
where previously there would be a mix of absolute, relative and
include path-dependent includes.
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.