Figure out when a record needs to be generated as a class

[Therzok]

There are a few scenarios where plain structs were defined as classes in managed land.

Note in this issue the cases where we need to generate a class instead of a struct for Record:

• GList:

// This native struct cannot be expressed in C#. We need to generate a wrapper class for the struct pointer.
struct List
{
    void *data;
    List *prev, *next;
}

// Managed then becomes
class List
{
     IntPtr native;
     // Methods which interact with the native pointer.

     // In case we want to provide unsafe access to the native data
     unsafe struct ListInternal
     {
          IntPtr data;
          ListInternal* prev, next;
     }

     public unsafe ListInternal *Native => (ListInternal *)native;
}