Tests for Gloas optimistic sync

We are working on Gloas optimistic sync in Lighthouse (https://github.com/sigp/lighthouse/pull/9934) and have realised Gloas payload invalidation is a bit subtle and that it would be great to have spec test coverage for.

The main complexity is that if you get `LVH=block_hash(A)` from the EL, then you need to find the first Full beacon block `B` descended from `A-Full` on the chain leading to the invalidated head, and invalidate every `ForkChoiceNode`/beacon block that descends from `B-Full`.

This has several implications (which would make good test cases):

- Don't invalidate any `ForkChoiceNode`s between A and B (there could be multiple beacon blocks between them with Empty payload status on the chain leading to the head)
- Don't invalidate the Empty branch descended from B
- If B _is_ the invalidated head, ensure the Empty branch remains viable

Start with the Gloas optimistic-sync work in Lighthouse PR #9934 and locate the consensus spec test entry point for payload invalidation. Add cases covering the A-to-B gap, B's Empty branch, and an invalidated head at B; done means the specified ForkChoiceNode and beacon-block branches remain or become invalidated as described.

Written by the indexing model from the issue text.