Draft: Explore isolating authorization-related logic from IssuableFinder

What does this MR do and why?

⚠️ Not intended to merge ⚠️

• Create a new container class Scopes::ProjectAuth
• Move the Project scope-building methods off of IssuableFinder::Params into the container class
• Restructure the methods a bit so we can clearly see dependencies and data flow

Next steps

• Validate specs passing/coverage
• Do something similar for IssuableFinder itself now that Params is done
• Try to identify global or "base" scopes that we would always want queries in this finder to resolve to
• Identify how the container class could be restructured to function more like a policy scope

References

Epic: https://gitlab.com/groups/gitlab-org/-/epics/19335