[Bug] Models in mgmt plane would generate "required+readonly" properties into its public ctor

[ArcturusZhang]

if we have this model:

model Foo
{
  a: string;
  b?: string;
  @visibility(Lifecycle.Read)
  c: string;
  @visibility(Lifecycle.Read)
  d?: string;
}

the correct behavior is that, we generate this csharp class:

public partial class Foo
{
    public Foo(string a) {}
}

but in fact, this generates the following:

public partial class Foo
{
    public Foo(string a, string c) {}
}

which is incorrect.