CSEC: isSubtype does not handle primitives properly

[mattcce]

The following code:

class C {
    public void r(String s) {
        
    }
    
    public void r(int s) {
        
    }
    
    public static void main(String[] args) {
        String s = "test";
        C c = new C();
        
        c.r(s);
    }
}

breaks with the error RuntimeError: Class String not declared.

The error occurs during overloading resolution; and is because isSubtype does not handle primitives properly at all.