Fix field_visibility not called for new-type aliases

[nyurik]

The field_visibility callback is now called in case of alias new-type and new-type-deref with the type name and field_name set to "0"

This PR allows generation of different accessibility:

typedef const char *  pub_var1;
typedef const char *  pubcrate_var2;
typedef const char *  private_var3;

pub struct pub_var1(pub *const ::std::os::raw::c_char);
pub struct pubcrate_var2(pub(crate) *const ::std::os::raw::c_char);
pub struct private_var3(*const ::std::os::raw::c_char);

Fixes #2966