Add pub to scene so components can be excluded by type_id

[rydb]

I'm working on a library that integrates moonshine_save to include some extra utilities for managing saving/loading components with moonshine_save, and one of those features needs to be able to exclude components by TypeID. However, deny_by_id() is locked behind SceneFilter, which is not accessible due to scene being private.

This PR adds pub to scene to allow deny_by_id() to be accessible.

[Zeenobit]

Would something like SavePipelineBuilder::exclude_component_by_id() (which would call deny_by_id internally) solve your use case?

If so, I'd prefer that option, so that SavePipelineBuilder has full control of SaveFilter. This is mainly to make future refactoring easier as needed.

[Zeenobit]

The changes which add the SaveFile should be a in a separate CL.

Additionally, I was planning to solve the resource issue in a much simpler way without the need for any resources.

Similar to save, save_default, and save_all functions, we could introduce a save_custom function which takes a system as its input, whose job is to return a save filter and trigger the save pipeline.

Then anyone can use that to get their SaveFilter and start the pipe with anything, including a custom SaveFile resource if needed.

[Zeenobit]

As of version 0.3.3, you can use a DynamicSavePipelineBuilder to feed a SaveFilter into the save pipeline from any system which returns a SaveFilter:

fn dynamic_filter(/* ... */) -> SaveFilter {
    todo!()
}

let mut app = app();
app.add_systems(PreUpdate, save_default_with(dynamic_filter).into_file(PATH));

Additionally, I've added exclude_component_by_id and include_component_by_id members to SavePipelineBuilder.