Fixes an issue where two types can collide in the cgen

[jmgomez]

When generating a header with --header and then using it from another Nim project to import the generated types, generic instances can collide and produce an error.
i.e. typedef MyGeneric[TypeA] typename typedef MyGeneric[TypeB] typename signature here cant be the same as they are different types.

This issue can be avoided by using the Nim type as part of the name which is what this PR does.

Update:
Encode types so MyClass[T] becomes typedef MyClass<NI> TY_MyClass_int; instead of Ty_QjHlYnbKApuWy39cRg7R7dw

Update 2:

struct seq_int { //seq[int]
  NI len; seq_int_Content* p;
};
struct TypeTest_int { // TypeTest[T] = object 
    NI Whatever;
};
struct cpptest_ObjectType { //ObjectType = object
    NI32 x;
};
struct Table_intint { //Table[int, int]
    char dummy;
};

[Araq]

Tests are red though.