This is consistent with the core Godot source code, and ensures the
license isn't detached from its original code when individual files
are distributed.
This is taken from the Godot repository, so formatting is similar. This
updates the style rules as well.
Also fix style in files to conform with this version.
Rémi Verschelde
Hugo Locurcio
George Marques
Bastiaan Olij
Nickolai Korshunov
Marc Gilleron