Add ptr() / ptrw() to the arrays, add missing String methods, add missing CharString method implementations.

[bruvzg]

• Adds ptr() / ptrw() to the arrays, and renames existing ptr to _native_ptr to avoid conflict.
• Adds ptr() / ptrw(), parse_utf* and utf* methods to the String.
• Adds missing implementations of length() and get_data() methods of Char*String.

[akien-mga]

I notice that here it seems to be private, while in all implementations it's public, is that intended/a problem?

And if it needs to be public, should it be renamed native_ptr()?

[bruvzg]

It has friend Variant to use it, and AFAIK it's not intended to be used outside Variant source. Moved it to the private int the hand-made headers for consistency.

[akien-mga]

I'm not very knowledgeable about the godot-cpp implementations but these additions and fixes definitely make sense.

[bruvzg]

Also, added move constructor / assignment operator to the Char*String, or something like this will result in double free:

CharString cs = text.utf8(); 
//do stuff with cs
cs = text2.utf8();
//do stuff with cs 

[akien-mga]

Thanks!