Split options holder class (#6527)

Split options holder class (#6527)

This PR splits the OptionsHolder class into separate holder classes for every options module and makes them directly accessible via appropriate Options::<module>() methods. We forward declare these new holder classes and thereby retain that we only need to recompile when we change an option module that is explicitly included.
All (generated) methods that previously accessed the old holder object are changed to instead use the new holder objects.
This PR does the bare minimum to do this change, further PRs will eventually get rid of all template specializations that currently surround our options class.