Add Godot 4.x support

[DmitriySalnikov]

It looks like PCK has been changed in Godot 4.

[nikitalita]

Indeed. They broke backwards compatibility and added two fields before the reserved fields, changing the header length. You can check how we handle it in GDRE tools here: https://github.com/bruvzg/gdsdecomp/blob/master/utility/gdre_packed_source.cpp#L192

There's an extra flags field as part of every file entry, as you can see here:
https://github.com/bruvzg/gdsdecomp/blob/9e8cbbde2afd48f4f4d979264ceea7ff6440077f/utility/gdre_packed_source.cpp#L286

[DmitriySalnikov]

It turned out to be a bit more complicated than just two new fields, but now I hope PCK Explorer supports Godot 4 PCK files.