Vector<>::_ptr is now typed and points to the beginning of the array rather than refcounting block

Created by: koalefant

Godot-s codebase is a breeze to work with. There is one thing, however that drives me crazy: every time I debug something and want to check content of a String I need to do a pointer arithmetic and a cast in watch window.

Therefore I propose to change _ptr to point to the actual array and be typed, and assume that reference count and size is stored before it. I hope that makes sense.