Fix generated ModelViewModel_ OnModelClickListener Setter's Annotations

[baoti]

Fix wrong setter method annotation for model builder.

Now, the @Nullable annotation on the method:

@Nullable
public TestCallbackPropViewModel_ listener(final OnModelClickListener<TestCallbackPropViewModel_, TestCallbackPropView> listener) {
  // ...
  return this;
}

The PR fix it to annotation on the parameter:

public TestCallbackPropViewModel_ listener(@Nullable final OnModelClickListener<TestCallbackPropViewModel_, TestCallbackPropView> listener) {
  // ...
  return this;
}

[baoti]

@elihart I make this change move @Nullable to OnModelClickListener parameter.

[elihart]

Thanks, I'll try to look soon

[elihart]

@baoti This is great! thanks a lot for the fix, and I apologize for the long delay in reviewing

[baoti]

That doesn't matter. Thanks! 😃