Fix helper methods for private fields of structs/unions

[kornilova203]

Currently this struct:

struct MyStruct {
private:
    int field1;
    int filed2;
};

produces this implicit helper class:

implicit class struct_MyStruct_ops(val p: native.Ptr[struct_MyStruct]) extends AnyVal {
  def `private`: native.CInt = !p._1 // incorrect name
  def `private_`=(value: native.CInt):Unit = !p._1 = value
  def filed2: native.CInt = !p._2
  def filed2_=(value: native.CInt):Unit = !p._2 = value
}

First field has wrong name (private instead of field1)
I suppose that implicit class should not contain getters and setters for private fields

[jonas]

Also note that Scala Native does not support C++.

…

[kornilova203]

Oops I thought that private struct members are allowed in C