feat: make scroll directive standalone

[kwiateusz]

As this app uses Angular v16 it's great time to make this standalone. Backward compatibility has been preserved but I've marked module as deprecated.

By the way, I've removed the unused service to keep code clean and put access modifiers in directive methods. I think they shouldn't be used as public but if I'm wrong I can revert that.

[orizens]

hi @kwiateusz
ngxis was once exported as a standalone component.
whats the motivation for not using it as a module?

[kwiateusz]

Hi,

Standalone components are becoming the standard, and on top of that, importing the directive itself is more transparent.

When importing a module, until I look in the code, I don't know if there is only the directive I need or some others I may not use and they only pump bundle size because of not allowing for the shaking.

I know it's not a case here but making this standalone doesn't provide additional work in further maintenance and follows angular way of providing things.